The main changes:
1. The biggest improvement is that it no-longer feels like a single-player game: All three major (free) updates have significantly improved multiplayer gameplay + their networking code actually works now (not 100% of the time but good enough if your internet is 4Mbps or better).
Depending on what you want from Elite Dangerous, this will either make it an entirely different game (i.e. much more fun), or it will make no difference at all, or maybe somewhere in between. IMHO for most people it will at least be some improvement. I do recommend playing in Open (rather than Solo), there is more risk, but once you understand the basics it definitely adds to the experience.
2. It's no-longer a buggy mess. Yes, people still find bugs to gripe about after each major release, but Frontier are usually good at fixing them quickly (when they're not away at a big show like E3 anyway).
3. The bulletin-board missions have also been slowly improved with each update. Nothing game-changing yet, but there is more variety than before. Frontier have hinted that the missions will be greatly enhanced in the future, so if the samey repetitive missions was your main annoyance (and you are mainly interested in a single-player experience) then maybe better to way for the next major update or two.
