The only poker game you'll play in Stacked is Texas Hold 'Em, but chances are good that it's all you'll want to play, and there's plenty of deep strategy to be found in cash games, single-table and multi-table tournaments. If you're good (or just want to find out if you're good), Stacked will feature fully-ranked online tournaments. Check your rankings in the MTV Stacked Masters series. If you've shied away from poker video games because people don't play "for real" like they would if money was on the line, this sense of online pride and community might make a difference.
One of Stacked's coolest perks is its save-game sharing with both PS2 and PC. Just connect a USB cable to the PSP, jack it into your computer or console, and you can transfer your career data between the two machines, picking up on one where you left off with the other. If you're playing on Xbox, sorry - at least you get Xbox Live support. Then again, all the other platforms enjoy online play, too.