You're probably going to want one with roll over and plenty macro/profile options if you like MMOs. One thing you really need to state though is what kind of key feel you want. There are many different types of mechanical switches now.
It also helps to know how big your hands are, as key size and spacing can vary. Other options are whether you want the back lighting specifically through the key fonts, or surrounding the keys as well. Some boards are also more spill resistant than others.
The only other things than that I can think of for now is whether you want an LCD readout, wired vs wireless, ergo or standard keys, and general size of the board.
Key layout can matter a lot to some though that also chat a lot on game forums, as typing is WAY easier on some boards than others. I just returned a Sentey gaming KB because it sucked at typing and had the typical narrow Enter key found on MANY gaming KBs (even expensive ones), which also can mean other keys placed where they normally aren't on an office KB. It was also a bit smallish overall for my hands.
I really don't shop in anywhere near that high a range for KBs though, I'm just suggesting details that might help others with experience in such product to assist you better.
Some popular boards that come to mind in the $150-$200 price range though are the Corsair Vengeance K70, Microsoft Sidewinder X4, and Razer BlackWidow. Of those 3, the X4 and BlackWidow have a traditional typing KB layout, while the K70 looks like it compromises typing efficiency.
That said, the Logitech G710 is mechanical, back lit, has a traditional KB layout, and is under $100. Not quite as popular as the other 3, but some might argue a better value.
I'll just throw this out there in case you change your mind on price range though. The Thermaltake (Tt eSPORTS) Poseidon Z gets my vote for overall best value in a mechanical gaming KB. It's only $70 (full size one with NumPad), gets great reviews, uses fast response blue switches, has a standard KB layout, and comes with a 5 yr warranty.
http://www.amazon.com/POSEIDON-Switch-Mechanical-Keyboard-Warranty/dp/B00MB0QMJ0/ref=sr_1_2?s=pc&ie=UTF8&qid=1436392817&sr=1-2&refinements=p_72%3A1248879011%2Cp_n_feature_keywords_browse-bin%3A3355985011%2C3766188011%2C3355984011%2Cp_n_condition-type%3A2224371011%2Cp_36%3A1253505011