And now, as of CL 3,454 I am Pool 3 complete. I began playing on Day 1 of the public launch, and I have been buying the season passes, but have not spent real money on anything else. I have probably missed dailies for somewhere around 10-15 days total, but have otherwise completed all dailies, and all gold has been spent on either credits or mission refills (excepting the launch week where I didn't bother to do my math and failed to realize the "fast upgrades" in the shop were complete ripoffs). First P3 was Crystal, last was Falcon, so started with a whimper and ended with a "meh". Thoughts on card progression generally are that the game is at it's best when you are mid P3. At that point you have acquired two or three "buildarounds", and have seen most of the cards available, so you've started to target specific cards that you're hoping for. At this point in the progression opening CRs is exciting because you never know if you're going to pull that Mystique to complement your Wong, or if you'll pull She-Hulk (I know she is only recently P3, but I'm using her to illustrate a point) to knock your Deathwave deck into overdrive. By contrast, early and late P3 progression largely feel bad. Early P3 is marked by a general "what the fuck is going on here" vibe where, if you're playing in ranks above 60, you probably have no reasonable/reliable way to counter the majority of decks you're facing, and even if you have the cards to counter the deck you likely lack the meta-knowledge to accurately predict the opponent's deck. Late P3 is on the other end of the spectrum; it's pretty easy to make a totally playable deck that can make it to infinite if you have access to 3/4 of P3, but it's boring to do so, and there's not much impetus to do so because the main carrot-on-the-stick of unlocking specific new cards has likely undergone significant diminishing returns by that point in the progression ladder.
I will also unequivocally state that non P3 progression has felt awful to me. The P4 cards that I have pulled were, in order: M'Baku, Absorbing Man, Attuma, Titania, Maria Hill, and Super Skrull. In the current meta, one of those cards is definitely playable, one of them is an edge case, and two of them are memeable, the other two are worse than most P3 cards. ALSO: 3 OF THEM ARE NO LONGER P4 DROPS. WTF.
I'd love to be able to comment on how P5 pulls feel, but unfortunately I haven't pulled any of them. On the upside this means I haven't had to deal with the disappointment of pulling Shadowking.