I've never played a long campaign, but I've played a bunch of one shots and short mini-campaigns, and I've played both DCC and its Gamma World-ish, post-apocalyptic spin off Mutant Crawl Classics.
The good:
- As @Whizbang Dustyboots mentioned, Mighty Deeds of Arms is a great mechanic for letting fighters have the sort of versatility that is too often reserved for spellcasters in D&D-type games.
- Spellcasting rolls make magic more of a wild card than an "I win" button.
- Playing and running funnels can be a lot of fun.
- There's a lot of variance in play; smart play and risk management are rewarded, and plans and actions are rarely certain.
The bad:
- Goodman Games, as a company, has lost my business over the Judges' Guild situation.
- High variance play means a run of bad luck can spoil your night. On more than one occasion I've had one-shots where my character contributed nothing of value, because e.g. all my spellcasting rolls failed and I lost my spells ten seconds into the session, or come out of a funnel with only an incompetent wreck of a character not suited for any class. That might be a welcome and enjoyable challenge... but it can also just be a real PITA.
- The use of unusual dice (even by RPG standards) does nothing for me, and I don't have any use for a d7 or d16 outside of DCC/MCC.
Overall, even if I set aside my distaste for Goodman Games I would say that there are better games in the OSR space, but it is good for capturing a particular sort of old-school feel.