2006 is a weird year for me, not hard though, I know hands down what my winner is. It's weird cus there are a ton of significant games I have but haven't played enough or dislike.
I hate, hate, hate oblivion, but I never tried to mod it. I played like 6 hours, hated the combat, the first person point of view you're forced into or can't click objects well enough, and got stuck on some part, hated the leveling. And then never went back to try to fix it. Of course this was like in 2012 when I bought it for $5.
Lego Star Wars II - the original trilogy release in 2006. It was awesome. But not quite enough for my top vote. Blowing up the death star in a lego x-wing was pretty cool.
I own total war medieval and heroes of might and magic 5 but haven't actually played either sadly... just part of my never ending backlog. So can't vote there.
Star Wars: Empire at war came out this year. It seems good but I honestly only played it a few hours before getting sidetracked yet again.
Neverwinter nights 2 - I liked this game, seemed like an interesting story, but ultimately the d&d rules killed it for me. I didn't understand what I was doing, I kept trying to play it like I did dragon age origins and it is nothing like that. Most rpg/action titles are just d&d inspired in that they do "rolls" for hits but they're really just percentages and they use similar stats and classes. NVN2 is like simulated d&d actual table top play with d20 rolls and stats and rounds of combat. In reality it's turn based, it just happens quickly so it appears real time. I kept moving my guys around and wondering why I was dying to these attacks of opportunity until someone explained it to me lol. Again I played this in like 2011 or something, not at release. It would probably be a really good game if I followed a leveling guide and learned what to do.
Zelda Twilight Princess is another one of those games I never finished and I don't know why! I got about 4 hours in, got busy with real life, never came back. Does that mean it sucks that it couldn't draw me back to it? Idk, maybe lol. I'd like to go back and finish sometime.
Also wii released this year, there has to be a shout out to Wii sports just for the bowling! That game was awesome! I mean motion control has kind of lost it's niche, it seemed amazing at the time, now VR is the new hotness. But when Wii first came out bowling was like the only really cool thing you wanted to try on it with your friends. We used to have people over just to check out the wii.
However my pick is completely easy for me. Though I played this when it was released on wii six months late in 2007, the original release was september 2006. It is The Godfather video game!
https://en.wikipedia.org/wiki/The_Godfather_(2006_video_game)
The wii version I guess was a little different, had a couple extra leveling perks/skills. But the main difference was the motion control. You aimed with the controllers and could swing them to hit people and pull of execution moves. Like to strangle a guy you shook both controllers together. I guess it was kind of silly but it was fun.
The game followed the Godfather movie plot where you're a new character not in the movies, but everything you do follows the movie plot. Like you have to go protect Don Corleone in the hospital from assassins and stuff. It was open world a lot like GTA series. You could go into various shops and demand they pay you protection money and then you'd take them over and they'd pay you every week.
To get them to pay you you had to intimidate them first. This part was cool, cus you would slap them around or break stuff in their shop and there was a little intimidation meter showing how much they'd pay. If you intimidated them more they'd pay more, but everyone had a breaking point where they'd lose it and not pay you at all and call the cops. And then you had to run or kill them and come back next week when they respawned lol. So the trick was push them as far as possible to get the most money. And then all had a special weakness like breaking stuff, physical threats, gun threats or whatever that would net you extra money.
Then you'd take the money and go find weapon dealers and do various side missions. Plenty of weapons to chose from like pistols or tommy guns or shotguns with various upgrades. the leveling was straightforward, get experience for killing enemy mobsters but you got more if you pulled of various executions or headshots and stuff vs just shooting them. Every level you got a point to spend on a perk. Some were passive and would like give you more money from shops. Others made you stronger or aim better or gave special abilities. You could also go buy safehouses and find a bunch of other things. I'm not sure if it's as deep as GTA San Andreas or GTA4, I didn't play those, but for me it was perfect amount of free rein combined with plot and story direction. It was just darn fun. I played it a lot, probably around the 100 hour mark.