My 2009 13" 2.53 ghz 9400m macbook pro can run half life 2 very smoothly at low graphics settings. Your standards are too high or your computer is faulty.
I dont think his standards are particularly high considering Half Life 2 is a good 7 years old now. And just as an FYI, the ThinkPad T43 I had at the time with a 1.8ghz Centrino, 1gb of ram, and a Intel GMA 900 ran it on lowest settings fluidly as well. (Though that was Windows XP, not Mac OS with it's terrible drivers, and port of the game)
Anyway, I don't have a 2011 as I figured the 320m would be more important than a i series processor and I absolutely love mine. I ordered refurb and have had this one since late April. It really has become my favorite computer of all time, surpassing the 12" PowerBook and the ThinkPad T61 4:3 I had.
I haven't had any issues with the machine so far. It holds up well even with moderate to intensive work (gaming, watching 1080p video). Battery life is about what I'd expect from it, I get 5 hours normally, 7 if I really try. It's quiet, and even so when gaming (at least compared to any sort of gaming PC).
That said I do have some slight issues with it.
First, the hard drives Apple use are absolutely terrible. Replaced mine very promptly with a much quieter, faster, and more reliable one.
Second, and this may be a non-issue for you, but, with a laptop especially I prefer matte screens. It's not so much I can't/haven't gotten used to it, but, in some conditions it really is unusable.
Other than that I've been satisfied by my 13". It really is a great machine.