The TL;DR version: Mechanical Keyboards use physical switches to register each key press, your old keyboard probably uses a membrane switch, which is why the keys feel a bit "squishy".
So let's get to the actual keyboard review:
First, this K70 is the first mechanical keyboard I have ever owned. Previously, I was using a Microsoft Sidewinder X6. Now, I will say this, the X6 was one of my favorite keyboards. I used it for a solid 3 years without any problems. Only recently had I begun experiencing a bit of extra "stickyness" with the keys, specifically the WASD keys which I probably have abused over the keyboard's lifespan. Other than that, the X6 was performing like a champ, I didn't really give a mechanical keyboard much thought... until I tried one at BestBuy.
The K70 is a fullsized keyboard, complete with a tenkey set and a detachable wrist rest. The wrist rest is a definite plus as the raised keys and the depth of the keyboard body itself makes gaming without the wrist rest a bit uncomfortable for those of us without gigantic hands. As a person who uses the tenkey number pad quite a bit, I am very pleased to have it included on this keyboard.
The K70 comes with removable textured keycaps for the WASD keys and numbers 1 through 6. When I first installed the textured keycaps, I was a bit worried that the raised keys would inhibit my typing a bit, but after a few minutes of use I didn't mind them at all. You can always switch them out with the normal keys using the included keycaps and tool, so that part is really up to you. My only gripe about the textured keycaps (which shouldn't be a gripe if I wasn't so lazy) would be the lack of the other symbols on the number keys. I had to think to myself a little bit as to which number was supposed to be the % symbol. Again, you can always stick those keys back on so it's really not a problem.
The keys/switches themselves feel great. The actuation point for each key is only a few millimeters for the Cherry MX Red, meaning that if you're in the heat of battle, you only need to slightly depress the key to get the input to register. For some users who aren't used to it, that could be a problem, but for the majority of gamers, specifically FPS and RTS gamers, this feature of the Cherry MX Red switch is great. You can quickly double tap a key and get precise input from the key taps. Those of us with stubby uncoordinated fingers may have a bit of a problem accidentally rolling over other keys, but if anything it might just train you to be more precise with your key strokes. The tactile feedback you get from feeling the switches depress and actuate combined with the different sound of a Cherry MX red clacking against the keyboard truly add to the typing/gaming experience. I've logged about 10 hours of Battlefield 4 using the K70, and so far the results have been fantastic. I'm not going to say outright that my KDR and my win % went up, but I can say that I've found a little more enjoyment out of using the K70 during that time. I really can't explain why, you just have to try it. It feels great.
The backlighting on the keyboard is quite well done. I know it's not a Corsair RGB, but the red backlighting really does look quite good. It's adjustable with 3 different brightness settings and also includes the ability to light only specific keys, either the default WASD and 1-6 keys, or whatever other set you want to pre-program yourself.
The overall look of the keyboard body is excellent. The black aluminum version that I purchased is quite sleek and might I say very pleasing to the eye. The design is very minimalist, and although it's not as minimal as say a Das Keyboard or a Poker, it does not have all of crazy and unnecessary design elements that a keyboard like the Razer Blackwidow Ultimate would have.
The K70 also has a USB passthrough at the back of the keyboard. The keyboard actually uses two USB plugs to connect to your computer, with one of the plugs being a dedicated passthrough. You don't have to plug in the passthrough if you don't plan on using it, but it's kind of nice to have it there as an option.
The K70 also has the standard set of media keys, the usual play, pause, reverse, and forward buttons. They're set in a slightly strange location, right above the tenkey set, which almost obscures them if you're looking at the keyboard from the wrong angle.
The K70 does not have programmable macro buttons. I will miss that feature from my X6, as it had an auto-run button which I sometimes used while playing games that required me to walk long distances (DayZ, I'm looking at you). I'm sure I can find a software solution for that or program it into one of my mouse's keys.
Overall, I'd give the K70 a solid 9/10. I've only had it for a week, but I can already tell that it will become my gold standard of keyboarding. Go do yourself a favor and try a mechanical keyboard out today. Your fingers will thank you.