I agree with the sentiment that so far episode four's been the best of the season. It's the only one I've bothered to watch more than once so far this season (I'll rewatch the others eventually of course but I tend to prefer watching new things even if the quality doesn't match up).
As for the Lava World episode, is was rather good. I like it a better than the first three episodes but I have a few issues with it. For one, I'm mixed on the conceit of this episode. On one hand, it allowed for some pretty creative moments and humor in here and I like the emotional core that brought the idea to life. On the other hand, when you get done to it, it wasn't as well paced as the other ones and I can't be the only one questioning the eliminations ruling. With Paintball, there's a pretty easy way to figure out how someone's been eliminated, this game relies entirely on the honor system. Sure when there's enough people around you can't lie your way back into the game but couldn't you easily do so if just one person saw you fall down or you touched the ground by yourself? Sure, in the former scenario someone could contest your story but that doesn't really qualify as proof, as that person could have easily been lying. This may sound like I'm overanalyzing things or whatever but this was something that was bugging me throughout most of the episode. But still, they had some pretty funny moments (Hickey was great tonight) and some nice creativity so yeah, I'm mixed.
Also, while Troy's send off itself was nicely done and Levar Burton's appearance got the biggest laugh out of me that episode, I feel this was kinda a weak episode to send Troy off on. Well, that may not be the correct wording of it but it was just an odd decision to have Troy's [supposive] final episode to be Britta & Abed focused rather than Troy focused.
Still looking forward to the rest of the season, even though I was initially a bit skeptical of the post-Troy era for really, pretty illogical reasons. Wonder when the animated episodes suppose to happen, been looking forward/dreading that one.