I know there is a lot to catch up on, in terms of metas that have been formed and glitches that have been exploited in level design
This is not something you need to worry about. NeoLemmix makes a point of
fixing glitches, so the most unfair thing you'll encounter in NeoLemmix levels is generally either "extreme precision needed" (in the worst of cases, this includes release rate precision) or "very obscure but fair trick is used".
In terms of where to start - if you haven't properly played the original Lemmings games yet, I highly suggest starting with Lemmings Redux. It's a community-built compilation pack of levels from the original game, reordered for a better difficulty curve, and modified to modern fan level standards (such as not having time limits unless really necessary, and not having heaps of unused space on the sides) as well as to guarantee solvability under NeoLemmix game mechanics; a few levels that have particularly serious backroutes also have backroute fixes.
NepsterLems (by Nepster) and Lemmings Reunion (by IchoTolot) are two excellent packs that need to be on your to-do list at some point. The key words here though are "at some point". If you're new to fanmade content, these two will be
way too hard for you. They are absolutely amazing packs though, once you're ready to take them on. If you want something a bit easier, my first two packs - Lemmings Plus I and Lemmings Plus II - stick almost entirely to classic Lemmings features, and have generally had very good feedback.
"Classic Lemmings features"? Well yes, all of the above packs don't make much (if any) use of new features introduced by NeoLemmix. I don't know of as many good packs that do off the top of my head - one recent release I've heard is quite good but not overly difficult is SEBLems (by Flopsy), I haven't played it myself yet though. I did play the demo, and was pretty impressed. My own packs, aside from Lemmings Plus I and II, also make extensive use of NeoLemmix features; Lemmings Plus III a bit less so than later entries (it uses a few new object types, but no vertical scrollers or new skills). Lemmings Plus Omega is quite a good pack for someone experienced with Lemmings but relatively new to NeoLemmix features. When you're ready for a new-features-using equivalent to Lemmings Reunion or NepsterLems, try Lemmings Plus Omega II.
Wafflem's levels also tend to be fun, relatively easy, and make extensive use of NeoLemmix features, so check those out if you get a chance. I don't know if they've been upgraded to work with the latest version of NeoLemmix yet, though.
