The FF movie may not have anything directly to do with the games, but none of the games up to that point had nothing to do with with any of the other games. Many of the games had very different mechanics and had only stylistic similarities or standard RPG elements. Also, the name wasn't just placed on the movie, you make it sound like Square sold the name to someone else who put in on an existing movie and not that they made there own movie division (which ruined them financially) and produced it themselves. It was from the beginning a written as a FF movie, and in general visual style and more so the underlying story it was very much like FF7. It used the Life Stream concept from FF7 plus it used a 'meteor' but as a second Life Stream. It was basically as much of FF7 as they could use while sill having it be and original story.
That is the standard answer about that movie by apologists, but the fact is that the games, while set in different worlds (and sometimes, different eras) all had numerous elements that carried over. Summons, Chocobos, Spells or powers, items, airships, and Cid to name a few. The only things that the movie had were a character named Cid (which, if I remember correctly, was spelled with an "S" in the movie) and a chocobo emblem on somebody's shirt (similar to the old crocodile shirts). It was set on Earth in the future making it pure sci-fi (no fantasy whatsoever) and I found nothing in common with even FF7!
Regarding the "original" format of a franchise vs. other formats, have you seen the Star Wars prequels? Have you played any Star Wars games? Most people think the new movies (which is it's original format) were not good, and a lot of people think games like Knights of the Old Republic are a much better use of the source material. These things are by the standard you are setting, not Star Wars, but although they deviate from the original they are often considered more Star Wars than Star Wars.
The Star Wars prequels, no matter how people feel about them, still maintained a healthy amount of elements (not to mention characters, locations, etc) that carried over from the original trilogy. KotOR was set in a completely different time period, far away from the timelines of the movie trilogies which allowed the developers the freedom to develop the stories while maintaining the key elements that make the Star Wars franchise.
Again, they did not start with a game and then decide long after to put the x-com name on it. They had the rights to x-com, an alien invasion themed game, and they made an alien invasion themed shooter. One could argue that there were no true X-com games past the first (which is really UFO: Enemy Unknown). Terror from the Deep was essentially the same as UFO just set underwater, so while it was really the closest to the original, really it was too close. By today's standards it's more like a fan mod than a sequel. Apocalypse had new aliens and a real time option, and I don't need to tell you how much farther Interceptor and Enforcer get from UFO. The point is, it is not unprecedented to deviate from the original. If they don't then it might as well be Madden 20xx, the same basic game every year with incremental improvements. This version is probably more like X-Com than Enforcer was because you will have a squad to give orders to and the cover mechanics of FPSs have come a long way and FPSs are a lot more 'tactical' than they used to be. Tactical.
Are you certain that they did not have a game in the works already that was seperate and later decide to throw the X-COM name on it? While we may not know the true answer, your suggestion of how they came about it is an even greater slap in the face as they have not shown any elements (outside of the Elerium) which even relate to the original game. As for the sequels, TftD was very similar with some minor changes (even the aliens were, for the most part, the same with different names) but it, as well as the sequels, continued the story of the original.
...But I don't even really disagree with you. The XCOM FPS is by any reasonable standard a spinoff. Like Mario Kart or Mario RPG. But the problem is that the previous series wasn't X-COM, X-COM 2, X-COM 3, X-COM 4, and X-COM 5. It was X-Com: Subtitle. So if they did the same format then it would be confusing so they have to go with just XCOM which makes it seem like it is the main series. All that is not really important. You said that you might have bought the game assuming you thought it might be good if it wasn't called XCOM, but won't because it's a "total scam of a game". How can it be a scam if no one has lied to you? You know it's not a tactical/strategy game and they never pretended it was, and if it is a good game then they are not selling you an inferior product. So what we're left with is a scenario where you know what kind of game it will be, and that it is of good quality, but you will not buy it for no other reason than it has (in your opinion) the wrong name. You said it your self, that it isn't about what the game is at all, only the name. That statement alone makes your argument about what your willing to spend on the game irrelevant. You're whole protest is based on the assumption that they think you will make a decision based on something trivial like the title the game is given, and ignore any and all other information about the game. Which is exactly what you are doing. It's an empty gesture to stand on a principal that is meaningless because of the superficial thing it is based on. Either way, they are not going to notice your $50 is missing.
Unless I see more (much more) in common with the original, I cannot even consider the FPS a spin-off! The one that never got released, that would have been a spin-off. This game has nothing in common with the original series as far as I am concerned... that is the scam!
You don't need to actually do any of those things. Although I didn't know about the clip thing at the end of the battle. I'll have to keep that in mind for next time I play.
No, you weren't required to move things around, but I found that I needed to as it always equiped my weakest soldiers with the Heavy and Auto Cannons. When they could only take one or two steps before running out of TUs, that would be a major problem. Especially if they were in the front of the SkyRanger when you entered the map, blocking your other troops from being able to get out. I always felt that if you could assign your soldiers certain "specialties" and they always equipped with the appropriate equipment, that would been a huge boost for going into missions.