You don't unlock moves as far as I know. You can unlock Steve, Alisa and one other character that I forget at the moment. Which makes me wonder, if they release more characters down the road, are you going to have to buy them and then play more to unlock the ones you purchased as well? That would be ridiculous so I hope not.
The ability to increase your stats (Strength, Health and Luck basically) isn't really much of a problem when you're fighting people around the same level as you because they will have attained around the same number of Skill Points as you, but of course they may have allocated them to different stats entirely. I didn't really notice it initially, but good players from previous Tekkens at level 0 who go up against someone who is like level 10 and has evenly distributed their skill points, struggles a bit more than you would expect. This is because the opponent will do more damage, have more health and chances of landing critical hits and rage mode are higher. So if that player manages to land in just a few good combos and a couple lucky throws....it can be over real quick. So if you're good at these games, and are just starting to improve your character, you don't have as much room for slip ups against n00bz as you would have in the past. I can see some people having a problem with this, but for the most part, if you're fighting people around the same level, the RPG elements make the game more interesting.
The only other thing I can see people really not liking, is the "coins" system. You have to spend virtual coins to play arcade mode and online. Arcade coins and Battle coins respectfully. You can only have two Arcade coins at a time, which replenish one per hour and 5 battle coins, which replenish 1 every half hour. There are also "premium tickets" and coins which will work for all modes. Tickets can be earned through in game tasks, coins can be purchased. If you win the battle, you get to keep your premium tokens. So if you want to play hours on end, you'll have to pay unless you're good. I can see the hardcore hating this aspect and I will agree that it's kind of a strange way to monetize the game.
Overall though, I'm having lots of fun with it. I might even pick up Tekken Tag 2 sometime in the next few months. That's probably what Namco is hoping for too.