Ah cool! A new release! (Sorta, not quite a full release at RC. It's like pre-beta afterall.)
Things I've noticed so far in my hour or two of early testing:
The good:
Seems less crashy when working with VST instruments. They don't seem to load that much faster, but so far it seems like there's some improvement in terms of stability. Old saves that have problems loading because of VST instrument related issues now seem to load better. Might have to investigate this more.
Mixdown seems to have changed slightly within the program. But the good news from that is that exported files seem more true to what you hear when you created it. (Which could be an annoyance at times in 0.4.12 and 0.4.13. Things could be off by thatmuch in those versions - yet enough to be noticed.) I don't think it's just me. So if bringing in a song you were working on, you might want to remaster (adjust volume levels and all that jazz) it before continuing in this version. The upside being that what you hear should be what you get. (Keeping fingers crossed that this is indeed the case.)
Multitrack export and looping export option. These are rather nice. Still new so I haven't explored these features fully, but I like them. This makes things much easier to master outside of LMMS. Multitrack is great if you feel you have more finesse with Audacity or similar, you can now work that way. (If your song is big, do make sure to make a new folder to save to first. It can get crazy with all the files, but it's doing exactly what it's supposed to do.) The looping export is also cool not just for making beats of known duration for mixing in some other software, but for tracks in stuff like games or flash apps - they synch better.
The bad:
If you're going to export something, you're going to export it. The cancel button doesn't seem to be working for some reason. Seems like a rather stupid bug, but stuff happens. It's RC version afterall.
???
Sometimes there's a little bit of a stutter on occasion. Not sure what causes it. (Converting part of an old .mmpz as it plays? It does says a track has been changed after playing once, even when I don't do anything to it.) Been replaying old saves in my testing. However it seems like it goes away after playing a song a second time.
At least this is the case in the Win-32 release as run under WinXP, since that's what I'm using. YMMV with Win-64 and Linux versions.