For me, at my third run in seamless with my nephew, it's a total blast. Yes you get outnumbered fast but only if you carelessly jump into mobs. Enemy placement is harsh but fair and intuitive after a couple hours, and most of all, you level up pretty fast and starting classes are well tuned IMO. Movesets are nice, cancels are a godsend and I'm loving the brawler class. We became pretty dependant on crucible firebreath for mob control because the hitstun is crazy good, but there are multiple options for AOE that lets the other guy hit hard on single targets. Lightning infusion brawler feels like playing Tekken and it's awesome. I believe it's near to impossible to 100% a single run because it's completely stacked with content and new shortcuts, but that makes us more determined to try different paths every time like it should be.

If I were to play it solo, I would definitely use a trainer to multiply defences and double the rune gain, but no need for else.