It's a high-end gaming PC. Sure, it's "great".
I wouldn't play every game at 2560x1440 though. Many look almost exactly the same at 1920x1080 but would allow higher frame rates or higher quality settings.
My general rule-of-thumb is that I play at 2560x1440 only if I can maintain 60FPS at max (or near-max) quality. You should be playing Crysis 3 for example at 1920x1080, and CIV5 or similar at 2560x1440. Top-down, "god" games tend to look better on high-res monitors due to the small HUD/text elements and luckily these games don't tend to be as demanding either.
Crysis 3 looks nearly identical at 1920x1080 as 2560x1440 (on the same 1440p monitor) but at a 30% performance difference so you'd have to lower quality settings or suffer a lower frame rate which results in a POORER game experience.
FYI, the "greatest" gaming PC's will be those using G-Sync monitors and that requires an NVidia graphics card so if that interests you I suggest something like the EVGA GTX780 967MHz ($510 USD).
Wasn't sure if you had a 2560x1440 monitor yet. If you did then you likely won't upgrade for a long time so G-Sync wouldn't be a big deal. If you didn't, it's still hard to justify as the Asus G-Sync 2560x1440 27" 120Hz model will be $800USD initially and you can get an Asus non-GSync IPS 60Hz monitor at same basic specs for $530USD.
DDR3 memory:
Unless you edit video, more than 8GB is overkill. You can get a good G. Skill 2x4GB kit for $65 USD through pcpartpicker.