Fighters don't get more confusing than this. While the game is a lot of fun to play, all you pretty much do is mash buttons to win. The controls in this game are terrible, so you'll have a hard time figuring them out.
Gameplay wise, it's like most other fighters. You can do arcade mode among many other modes such as multiplayer, practice, and so on. There's little to no story to it. It's like they made a 2.5D version of SSBB but removed the story and the characters. The fights are mostly tag team, which means you and an AI (unless you're in multiplayer) fight against other AI opponents. If you're on low health or in any other situation, you can switch to your partner. Either that, or you can just let them get a free attack in to get a jump on your opponents. I found the character roster to be unique. You get some Capcom characters like Ryu, Chun Li, Mega man and even his friend Roll. I usually play as the Tatsunoko characters, who are more interesting and have much better move sets.
Now, about the horrendous control set up. It's border line unplayable if you use a Wii remote and a nun chuck. The first time I played the game, I used this combination, and man was it terrible. I triggered random special attacks with the slightest waggle of the remote, plus movement was hard. I then tried using a Game cube controller, which was easier but still frustrating to use. The controls made more sense, but I couldn't remember them well, so I frequently had to look them up. On a better note, the special attacks looked marvellous, with a lot of flashy effects to go with them. They did a hefty amount of damage too (some attacks cause over a billion damage). The tag team aspect of the game was in my opinion, a smart idea. It made fights longer and more fun, and could cause some heroic comebacks.
Once you win fights, you can earn currency called zenny. Zenny can be used to purchase Tatsunoko and Capcom related things in the in game store. There's an online mode in this game, but it wasn't as pleasing as the single player in the slightest. It had two major problems. First of all, it was almost impossible to find a match, I found around 5 matches in a week or so. What's more annoying, however, is how unbalanced the matches actually are. My first match was against a professional, who, of course, beat me over and over again. The matches would of been ok if they were actually ranked, so you had more of a chance to win.
Tatsunoko vs Capcom is a good fighter for the Wii. The controls and the lacklustre online mode can hamper the overall experience, but if you don't care about the Wi-Fi and have enough patience to learn the controls, then there's a lot of entertainment here for you.