I'm currently developing an LOP based MUD so let me try to answer.
Lands of Pabulum is a basic stripped down version of SmaugFUSS 1.7, built back up again with added features and fixes. I say stripped down because it does not come with the dozen or so area files that are supplied in SmaugFUSS, it only contains the two main required areas, which is good in my opinion as it allows you to build and develop any theme you'd like. When I think Smaug I think medieval fantasy but even the existing main city area can be easily adapted with the OLC to anything your imagination can think up. SmaugFUSS areas are not compatible but there is an area converter if you'd like. Building is very easy and I've written a building guide to note the differences from Smaug.
LOP is very stable and is one of the most actively developed and supported code bases here thanks to Remcon. As you can see from posts he is very helpful and very quick to make fixes as they are reported. He's almost ready to release a newer version as well.
As for the features, take a look at the file repository for complete lists of changes, additions, deletions of the code. Look at each release, because there is a lot of work done in each. Or, download it and try it yourself, that's the best way to get a feel for a code.
Feel free to drop by my MUD. I'm usually there but I do idle a lot if busy with other things but you can browse around (alm-dev.org:4000)