I had a 2G/3G Defender case on my previous iPod Touch 3G, which is now my wife's since she got me the 4G for xmas. The new 4G case feels pleasantly thinner than the previous model (which felt a bit too chunky), but I hope it has the same level of protection. I've dropped my previous iPod accidentally from counter height onto tile floor and it's been fine in the 2G/3G Defender case, and the new thinness of this case makes me wonder if it would protect as well (not intending to try).
As others have mentioned, the sync port and headphone dock flaps on the bottom are more difficult to get to stay in, and flop out easier, which is frustrating enough to almost give this 4 stars instead of 5, but that would be unfair to other people looking to compare this great case to other lesser cases. The 2G/3G version of this case completely covered the iPod and stayed covered unless you deliberately opened the port flaps. This case has 4 unprotected holes: for both cameras (front and back), for light sensor, and for the speaker (next to the ports). Not sure how I feel about that. Will probably let more dust/dirt in, and the new hard plastic case is much harder to take off than the previous one for cleaning.
On the plus side, the new protective screen exhibits no oilslicking like the old one did (see talcum powder workarounds for that on the old one), but the new one has already picked up a few light fingernail marks from my relatives playing angry birds on it.
The pad for the power button does make it easier to press, but the volume pads require substantially more force.
I've had it now for a bit under a week, and it's still a wonderful case, like the previous gen version, with the above caveats. 4 stars comparatively, 5 stars compared to other cases.
UPDATE: After using it daily for a couple months now, I've dropped this from 5 to 4 stars, as the silicone wrapper keeps slipping, and buckling up a bit on the hard inner case. This combined with the flaps issue, regular dirt accumulation through the holes, and a bit of tactile (not audible) creaking of the plastic case, compel me to 4 star this instead of 5. Don't get me wrong, if I lost it, I'd replace it with another one, and it still protects very well against drops and bumps, but it seems a few needless things were shortcut when designing this.