I already have #3 and enjoyed it, but I'm curious if any of those other bundles are particularly recommended?
I could look them up game-by-game on Steam, but that would take longer than actually playing some of those games and be less fun. :)
#4 - I adored the Twisted Lands games, but they're really love 'em or hate 'em games due to the open-to-interpretation and sometimes confusing storyline. I personally love the "What the hell??" aspect to the games XD
The Enigma bundle probably has the best games, overall. The House of 1000 Doors games are VERY popular, and the Brink of Consciousness games are some of the best IHOG's I've played. Nearwood was excellent, the second-best IHOG of that year (with Enigmatis: Mists of Ravenwood being voted #1) I played them both and loved them both.
Sacra Terra: Angelic Night (which you've probably played since you have #3) is another personal favorite.
#2 - I didn't care for the first Weird Park game, so I never tried the 2nd and third in the installment, but MANY loved the series. Dreamscapes: The Sandman is one of my favorite casual adventures.
#5 - Cruel Games was a lower-budget game, but I also think that it deserves more attention than it got. I really enjoyed it despite some small gripes. Lake House: Children of Silence was very enjoyable for me, Theatre of the Absurd has some irritations to it, but I still really liked it, and Voodoo Whisperer: Curse of a Legend is another I had fun with. The reason that it has mixed reviews is -- I'm sure -- because it has a cliffhanger ending. I still recommend it ;D
SO, I would say definitely to the Enigma Bundle, #4, and #5 (my personal opinion, of course)
EDIT: I have reviews for many (if not all) of the games I mentioned, so let me know if you'd like to see them!