I too am a fan of 1st/2nd edition. I really did not like 3rd edition it felt like WOTC was spoon feeding RP to the players. The only experience I have had with 4th edition was Neverwinter MMO.
There are some good things that i like about 5th edition, mostly the spell slot/prepared spell concept, i find superior to 1st edition.
As, far as multi-classing went it was a trade off for demi humans to be level limited, a concept I always thought counter-intuitive, you live 1000 years and your stuck at level 11?
Also there was no level limit in 1st edition, well besides the afore mentioned demi human issues.
So in 3rd edition people made the stupid decision to limit all races to level 20, and to allow all races to multiclass, which was not a good change in my opinion, as it puts an artificial end to the game, and eliminates the individuality of the races.
1st edition had some minor problems. That could have been reworked and fixed, without completely changing the game. For instance armor for mages, leather armor weighs like 15 pounds, and a mage, with a strength of 9, and even lower, would not be able to wear leather armor as it would make it so he could not carry anything else and move at a decent speed. The logic that elves use special "elf magic" was a stupid workaround, and the idea you needed to be proficient in putting piece of leather on that was basically a flak jacket, was also stupid. Then you have the argument that armor interferes with spell casting, except leather doesn't as it does not include gauntlets and thew DMG describes somatic components to be on par with what you see in the tv the magicians.
There were some other issues, that after i grew up and had done my own research i realized did not make sense.
The beauty of 1st edition dnd was the homebrew campaigns. I always allowed my mages to wear any none metallic armor, and even allowed monks to wear light armor, and keep the dexterity bonuses that were stripped from them.
Early game survival in 1st edition was very very low.
