Prepare for many varied replies, the most honest answer is "that depends" on how you want to play
40k.
The "bad":
For pick-up games or meeting with strangers to play it is problematic possibly unsuitable (points costs are rather unbalanced).
For competitive play, it seems to have a bit too much dependency on randomized rolls at the cost of tactics: army lists are the main basis for a win or loss.
The ability to play "unbound" and dependency on "maelstrom" for objectives leads to some rather comical combinations.
Many character abilities or psychic powers blended with units from other factions have lead to some challenging "death stars" in the game.
Formations are now more the focus than your specific army selection. Many free bonuses have been sources of contention.
The Sisters of Battle have been ignored for so long it is bordering on the "Squat" situation (Orks are hanging in there,
IG/
AM similar,
CSM it remains to be seen with the new rules).
You will no longer see rules for models that do not exist already or not with the release of the codex/suppliment. Lessons learned from the "Chapterhouse" court case.
The "can go either way":
Many elements of Apocalypse rules have been formalized into the main like "Lords of War" units.
There is a separate psychic phase which for fantasy players is no big deal.
The old/new (not sure what to say) White Dwarf magazine is back to what it was/is so hopefully can be a good single-source for updates.
If you play Eldar or Tau you are a very happy player since their rules make winning the game a little easier (balance).
Aircraft are a big component of the game more than ever, the newer "Death from the Skies" seems to represent non-mandatory rules... remains to be seen where this goes.
There have been so many releases of paid documents (codex, supplements, warscrolls, formations) it is bordering on impossible to collect them all never-mind afford. We are more dependent than ever on your opponent knowing their rules and not fibbing.
The "good":
GW has started offering more box deals and mini-game deals that are very nice and compelling. They are the #1 exciting element of releases at this time.
Some truly nice plastic models have come out and made the game very exciting with factions that were discussed but never represented till now.
Now more than ever, it is possible to represent pretty much any mixed force you would want.
"Fluff" players can be quite pleased that pretty much anything can be fielded.
FAQs have started being updated again!
Forge World rules and models are "official".
30k many people are looking into where it has been claimed to be a more "balanced" game plus the older style spruced up a bit is looking good.
There is now a bit more blending between the two eras (35K??) so units can fit into the
40k system.
I think it really comes down to what you are looking for in the game.
If you have a bunch of friends to play with a certain "armistice" or house rules can tame some of the balancing.
Someone willing to have a go at scenarios can smooth out the rough spots in the game.
The "Kill Team" rules can be a fantastic way to get back into the game rather cheaply and get the game down to the size of battles it seems to be designed for.
My opinion of course.
Good luck!