This case is not particularly hard to open. The thumbscrews are definitely easier than regular screws, the lip for your fingers at the back gives you plenty of leverage to pull the door off, and the mounting clips themselves aren't of the highest quality, but are certainly not of the lowest quality either.
Removing the front panel will pucker your arse up though - it seriously feels like you're about to break it right before it gives. The top panel is also a bit tricky, since you have to sort of lift both sides of clips off to remove the top panel, then "walk" the top off. And it might just be because my cooler is so big (horizontally), that it is nearly impossible to reach the rear clip to release the top of the case with a top fan installed. If I didn't have the Thermalright SI-128 SE this probably wouldn't be as much of a problem, but even so with a fan installed you're going to be pretty close to your motherboard while you're poking around in there.
And if you're shopping in April, I'd probably pick up the Cooler Master Centurion 590 if it's out by then instead of the RC690. I'm starting to get the feel that the "RC" stands for "release candidate", and we're all sort of test dummies for this case. Personally, there are a few (very cheap) changes that I'd make to this case to make it more appealing, like raised and thinned hex mesh over the fans to prevent fan blades from impacting the side of the case (it happened to me), as well as keep airflow noise down. A raised cover over the top fans would have been very nice as well, something like the P182 has. Those two things alone would be enough to turn this case from good to great. And if they made it in aluminum...ah, I'm getting ahead of myself.
Overall, I really do like this case. The cooling power is exceptional, especially if you're using a downdraft style cooler like I am, since you can mount a fan right over your CPU fan, and even have one exhaust out the other side (which I have yet to try). Overall, there's definitely a reason this case is cheap though - Cooler Master cut every corner they could to get a full-featured case like this as cheap as it is. No case speaker, rather cheap and flimsy fan filters (my bottom filter isn't even properly fitted - when it's screwed in, the fan holes in the filter don't line up with the case), the fan mesh problems I stated before, the slightly cheap feel of the mesh and chrome bits, the rather shoddy case buttons, etc. all add up to make this case feel like a $30 case with exceptional cooling power, cable routing, and general features. If I were to compare it to a car, I'd compare it to the Toyota MR2 MK II. Sure, it's a midship-engine, rear-wheel drive car that feels very snappish and fast, but it's definitely no Ferrari. Of course, it's not priced like a Ferrari either, which is why it's very easy to forgive.