First being the hidden information, you don't know your opponents hand holdings; that is to say everyone in the game has a different information set.
The second is that there's a variable number of players in the game at any time. Heads up games are closer to solved. Mid ring games have had some decent attempts made. Full ring with 9 players is hard, and academic papers on it are sparse.
The third is the potential number of actions. For no limit games there's a lot of potential actions, as you can bet in small decimal increments of a big blind. Betting 4.4 big blinds could be correct and profitable, while betting 4.9 big blinds could be losing, so there's a lot to explore.
>>Is limit poker a trivial game? I believe it's been solved for a long time already.
It's definitely not trivial. Solving it (or rather approximating the solution close enough to 0) was a big achievement. It also doesn't have a deterministic solution. A lot of actions in the solution are mixed.
