The jungle set, as I said, is nice, and the Doctor and Romana make the most of exploring the odd eggshell that the TARDIS materializes near. And the wolf weeds are frankly much better than one might have expected; the rolling motion helps sell the effect and demonstrates that they're not just being dragged around with strings. The other good thing about this episode is Myra Frances as Lady Adrasta. She's playing the part with very serious intent, and so the danger seems much more plausible than in other stories. The same can't be said for the bandits who've captured Romana, though; writer David Fisher appears to have made them deliberately stupid for some unclear reason, and so while it's entertaining to watch Lalla Ward command them imperiously, it does make for some rather labored comedy moments later on.
But still, this first episode is quite well done, and the cliffhanger's pretty good too (even if you get a sense that none of the actors quite know how to play the scene leading up to it). It's in the second part that things start to slip. Lady Adrasta remains wonderfully straight with her villainy, but the Everest in Easy Stages bit with the Doctor is incredibly lame; at least when they did something similar in Destiny of the Daleks it was an in-joke. Of course, things improve rather when the Doctor meets Organon, a seer, at the bottom of the pit; Geoffrey Bayldon pitches his performance just right, and he gets some great lines ("Organon, sir. ... Astrologer extraordinary. Seer to princes and emperors. The future foretold, the past explained, the present... apologised for"). But then we get our first view of the eponymous creature, and it's... ah... worryingly inappropriate-looking. It's a bit better when we can see more of this gigantic thing (thanks to CSO shots), but there's still a green fleshy pseudopod probing the air in front of it. To say it's not realized well is a bit of an understatement.
The realization isn't very good, and there are some misjudged comedic bits (such as anything involving the bandits), but so far there's enough here to keep viewer interest. It's a nice touch, having the Doctor not be afraid of the creature or consider it evil automatically; if things continue like this, The Creature from the Pit might work out okay.