To start with, there's simple probability: knowing the odds of making you hand vs. the payoff in the pot, or the chance of winning with various starting hands. This is pretty basic but a lot of low-stakes players screw it up. If you get it right, their mistakes are your gain.
At a more advanced level, game theory comes into play, using bluffs and so on. The game is complex enough that it's not completely solved, and it's an active area of research. The University of Alberta is doing a lot of working developing poker bots using game theory. By playing a good strategy, you can prevent other players from exploiting your patterns.
Only after you've got a good grasp on all that should you really think much about exploiting a particular player's weaknesses. The Alberta guys are doing work on that part too. Exploitative play can improve your profit but also makes you more vulnerable.
For a good overview of this stuff, the book Mathematics of Poker by Ankenman and Chen is a good place to start.
I agree though that HFT is awfully competitive these days. If I had to choose between the two I'd play poker.
So true, and frustrating. But, the legalization of online play could bring back another boom at least for a couple of years.
Poker is "a game of skill with an element of luck" and should not be confused with say, gambling on roulette or the outcome of a coin toss.
But the HFT game changes and you have to keep up. Just as a poker player from 10 years ago would not survive in the game today without adapting his style of play.