But you seem to be assuming that tactical play means freedom of movement and placement. I'd argue that it's more about using the terrain that's available to you to gain the biggest advantage.
There's nothing interesting about taking a city if there's enough space around the city to fit 20 units. It would be akin to taking Civ4's stacking, and adding a per-unit micromanagement layer on it. There would be nothing interesting about city placement, there would be nothing interesting about chokepoints, there would be nothing interesting about natural barriers like coasts and mountain ranges, because there's always enough room for your units. It defeats the purpose.
The gameplay doesn't become interesting until there's not enough room for your units, because that's when you have to start making decisions.
I think you're conflating tactical gameplay
in Civ 5 to tactical gameplay in other games. I agree that Civ 5 doesn't become "interesting" (or at least require a bit more thought) until you have limited approaches and are forced to decide which units lead the charge, and where to stick your ballistic units.
But that's not really tactical gameplay.
Tactical gameplay involves a LOT more than freedom to place your units, because it requires a LOT more space to pull off effectively. Tactical gameplay involves things like unit facing having an effect on how much damage the unit takes in a given round, lines of sight (and manipulation of them via things like moving in cover or a reverse-slope defense), morale and command & control features (IE: your unit cannot effectively respond because it's too unconnected from its commanding officers and cannot be rallied in the face of heavy enemy fire), the art of maneuver (IE: actually flanking an enemy and having it actually matter -- see the bit about unit facing), covering fire (IE: you can destroy a unit's morale simply by firing enough AT it even if you don't HIT it -- like making it afraid to advance because you've got a machinegunner firing at it every time it pokes its head out), opportunity fire (IE: it's not your turn, but your unit has extra "moves" left, so if an enemy unit enters its line of sight during the enemy's turn, your unit can fire on it), and so on and so forth.
Tactical gameplay is very nuanced, and very complex. The gameplay in Civ 5 is not all that nuanced or complex, but it incorporates certain tactical SCALE elements with 1UPT.
The Civ series has often incorporated terrain bonuses, too, which are also part of tactical gameplay, but it was frequently very very simplified. IE: a unit on a hill gets better defense values. Well, in a true tactical game, that unit would have far more of a tactical advantage. It could be able to both fire and see farther. Units approaching it could tire and/or suffer morale penalties (and be more likely to rout) by advancing up the hill. It could also be exposed more to things like artillery fire (whereas hiding BEHIND the hill would help hide it, and provide other benefits). Civ just gives a "+X bonus to defense."
The problem here is not that we have tactical gameplay, but that the gameplay is NEITHER tactical enough NOR strategic enough. They didn't go far enough in either direction, so what you end up with is a strategic game that forces very limited tactical movement, and/or a tactical game that confines your movement by forcing you to play on a strategic-scale map.
Put simply, the two parts just don't fit together. Not like this, anyway. A better approach would be a split between tactical-level gameplay and strategic-level gameplay. Towards this end, Total War and Master of Orion offer the best examples that I can think of. In both series, you build your fleets (stacks, in Civ), and maneuver them to an enemy position. Upon engaging the enemy, you're taken to the "tactical view" which is almost a whole separate tactical game (in Total War, a real-time combat game, and in MOO1 and MOO2, a turn-based game). Positioning still matters at the strategic level (IE: this star system or province is situated such that it acts as a natural choke point -- similar to the Dardanelles or Gibraltar), but the tactics of the game are far more nuanced.
There seems to be this notion that Civ 5 somehow added "tactical" city placement. It didn't. Heck, as far back as Civ 2 you could place cities in locations that would act as choke points (back when we had ZOCs), and everyone who played Civ 4 knew the benefit of building a city on a forested hill surrounded on three sides by river tiles. Those are strategic concerns which can ALSO play out at a tactical level if you model your map the right way.
What we've got here in Civ 5, though, is tactical-level unit management on a board that doesn't fit that scale of movement. What's more, it's not even entirely clear as to WHY this change was made.
Was it to discourage combat? Maybe, but if so there are far more elegant, natural ways to do that (IE: resource limits, stacking limits other than the extreme 1UPT approach, supply line modeling, increased war-weariness, costliness of waging war, etc., etc.).
Was it to add depth to combat? Well...it doesn't. Not really, anyway. It adds headache, that's for sure, but it's pretty simple to figure out that you stick your melee units in front of your ranged units and your cavalry on the sides. Duh. The only question is how to best do that given the limited space you're dealing with. Trouble is, on a tactical level, that's ALL you're doing. You're NOT doing any of the other stuff I described above. What's more, it's not even all THAT different from stacks. You just have less space to bring a big army into, and battles take WAY longer now. As otehrs have mentioned, in Civ 4, I'd build a mixed stack, move it into place, and then bombard with artillery units, followed by maybe softening up with ranged units, followed by attacks by my melee units, with some defensive and/or medic units to keep the stack safe should it be attacked. How's that any more or less complex or deep than "I stick my melee units in the front, my ranged units in the back, and my cavalry on the side"?
I'd also pay attention to positioning on the board. I'd try to approach a city so that I didn't have to cross rivers, or I might position a bombarding stack on a hill across from a river, while I moved the actual direct attackers to a forest tile without a river crossing. How's that any more "tactical" than what we have now? The only real "tactical" element that we have is the scale of combat by forcing each tile to only hold a single unit. You could still get just as much bang for your buck out of ranged units by moving them in a stack. Ranged units would still have a unique benefit, in that they could fire on units that are out of range of the melee units.
Anyway, I'm not saying that tactical gameplay can't be fun. It can -- when it's done right. It just wasn't done right HERE. I suppose there's folks out there who like 1UPT for whatever reason, and that's fine, but it strikes me that the game should have shipped with an option to turn that feature on or off (or shipped with a built in mod to do so or whatever). Although there are plenty of OTHER things the game should've shipped with too that it didn't include.... (IE: an Earth map with proper starting locations....)