This game has three selling points. First, the humorous dialogue. The dialogue between the characters while you play the game is very good. If you do not know the characters (or only know the Heavy), you will find the dialogs less meaningful. Also, after a while, the dialogue starts to repeat itself and the same things are being said over and over to ad nauseum. Thankfully, you can turn it off once you reached that point. Second, is the TF2 items you can unlock. The TF2 items are all purely cosmetic and are all either non-combat items such as apparel or different looking variants of already existing weapons. Third, is the low $5 price. Is it even worth that? No, there are much better ways to spend that $5, considering how there are sales on Steam frequently.
The gameplay is very shallow. Poker, in real life, is mostly luck. The only aspect of skill in poker is bluffing and discerning whether or not the opponent is bluffing. Of course, on a computer screen, you cannot read body language, removing most of the skill out of poker. This makes Poker NIght a luck game. Think of it as tantamount to a Mario Party game without minigames (just the board game). You aren't playing against human players. You just play the AI, and the AI is not very intelligent. Essentially, your main goal in playing this game is to exploit the painfully stupid AI.
There is only one type of poker you can play: Texas Hold Em. That's it. No 7-card stud; no five-card draw. Just one type.
Most likely, you will find yourself playing this game for 3 hours (if you can stomach it) and then never touching it again.