Most of my experiences with 4e came in the first two years. (In retrospect my campaign probably ran closer to two years of monthly play.) At that point, solos were not particularly inspiring and my attempts at using them were fights that went on far too long but with no one in danger of death. I tried running some higher level elites and they always died exceedingly fast.
I hear they fixed that in MM3 and later books but it was too late for me.
IME a lot of the earlier monsters were fine too, but there were some bad ones, and a lot of higher level ones that were just mediocre. There was definitely a learning curve where it took them a year to really get it down hard once the game was released. Still, I use plenty of MM1 monsters today and they're fine. Sometimes I up their damage a bit or whatever, but mostly if you put them in interesting situations then they're fine. The MM3 and on versions are always EVEN BETTER of course. The same is true for MM1 solos. I actually ran an MM1 adult white dragon fight early on, and it was pretty good. I threw in a bunch of chillborn zombies and stuff like that and had them frozen in ice pillars that would get smashed during the fight, there was glare ice, and pieces of roof that would fall. It would be a lot better with the new White Dragon I'd guess, but the old Solos were workable, at least at low-mid level. You had to add action denial recovery tricks at high levels, but MM2 came out by the time we got there and had some usable designs.
I would say this, the 4e monsters weren't the best ones ever starting out, mostly, but WotC followed through and kept iterating better designs and wasn't afraid to roll out replacements. Contrast with the 1e MM where the monsters were not bad, a mixed bag from great to kinda bad, but they never tweaked any of them based on lessons learned. We didn't get improved versions until 2e (some huge improvements), which was kinda a long time to wait.
Part of the problem is also the ease of the combat rush. I know a LOT of 3e-4e fans stumbled with this when they started playing Next and the Caves of Chaos. The inability in that story to just charge into a fight. We've had two editions that have taught players that unless your DM is a colossal dick the fight will be fair and balanced. With 3e there was still the chance for some strategic element, where you might be better off holding back the charge until you buffed a few rounds. In 4e, with most buffs being combat buffs there was seldom any reason to delay except to allow the defender and controller to go first to really handle the fight.
This made investigation and alternative-victory combats hard (and still hard in my Pathfinder game).
Eh, I dunno, when I did Caves of Chaos we didn't literally just run in, we snuck up, ganked the outdoor kobolds, avoided the orc cave trap, chose a direction that had seemingly less orcs and just went for it. We'd barge a door and just take them. That was the first playtest packet, so maybe it was different later. It wasn't quite totally mindless charging in, but IME that isn't a real winner in 4e either. Triggering 2 encounters at once is bad news. See the famous Iron Tooth encounter in KotS where you get ganked for that right quick.
4e does have daily buffs, which will last 5 minutes, but there aren't a ton of them that you want to use before a fight. That role is played more by potions than anything else in 4e. That and some rituals. You'd also use story means (getting some allies, setting an ambush, etc). I always found the AD&D/3e buffing ritual a bit formulaic once you did it a couple times. I think there could be a shift in balance back in that direction some, because for instance it means weaker monsters can be a bit more challenge, you don't waste your buffs on them, so it can help a bit with quicker skirmish type fights. Its fun too, and 4e did seem to de-emphasize it. You COULD still play that way, it just wasn't the only sane way to go.