Hiya!
(Quick note to
@mrswing ; I think your DM ran "UK3 - The Gauntlet" incorrectly; it's basically a "siege" where the PC's are sort of caught in the middle; the 'arriving forces' want something from the 'defending forces' in the Keep and ask the PC's to do it for them...if they do it, the 'arriving forces' leave; so, basically, the PC's aren't really supposed to try and massacre everyone in the Keep...or outside the Keep; anyway, this is just my interpretation, as I never DM'ed it...got close, but the PC's chose other paths)
Now... 5e Combat is "Generally OK". The biggest problem we had/have is once PC's even get close to 'mid level' (for us, that's 5th), the "solo" bad guys HP pool is just way to much with very little 'actual' threat from them....and it can easily turn into a slog. I have toyed with simply lowering HP's, but think simply adding some more "deadliness" to combat would be better. Which is... you get a Critical if you hit your opponent by MORE than 5 points. If you do that, double damage. If you do that AND the roll is a Natural 20, you
maximum double damage. This may cut down on the HP's faster...and make the creature a bit more deadly! But...never tried it yet. Maybe next time I DM.
I prefer Hackmaster 4th Edition combat the best out of all the "D&D systems"...with BECMI coming in a very close second. I have 'simplified' HM4 combat in some minor respects (Armor HP's only go down by the amount of dice damage minimum; e.g., 2d6 weapon takes of 2hp and only on a Critical, for example). But the "Penetration Damage", "Follow-through Damage", "Threshold of Pain", "Fatigue", "Spell Mishap", "Fumbles" and those
lovely "Critical Hit Tables" make combat so fun and often unpredictable!
Compared to HM4 combat, 5e combat is watered-down gruel. But then again, it isn't called HACKmaster for nothing!
With 5e, the combat is supposed to be 'exciting, but not any more important than anything else'; meaning the PC's are generally "supposed to win in a few rounds" except for the 'major' fights. Different design goal. Not bad, but, well, "Generally OK".
^_^
Paul L. Ming