As a heroin addict, and a previous meth addict (clean of that for years now) I will say the following:
The actual high is definitely over-rated.. I mean, don't get me wrong, a strong enough hit will get you completely fucking smashed so you can't see straight and you're fading in and out of wakefulness, having difficulties distinguishing between conversations in real life and those in your dreams/nods (oh god how I miss those days).
But, it's nothing like how fucking high you can get from other drugs, like LSD, MDMA, 2C-X, etc In fact, as far as 'vanilla' sort of drugs go, I actually prefer the rush of IV meth, to IV smack, but IV'n meth every day is just not something that sustains any reasonable description of life.
But - it's soul-destroying reputation for addiction potential is NOT over-rated.. It is difficult to even describe the ways in which this drug gets its hooks into you. And whilst certainly not everyone who tries it will become an addict, not even the majority, for those that do, the rehabilitation rate is tragically low.
All this said, I've never really messed around with other opioids, I take some OTC stuff when I'm hanging sometimes (codeine, etc) and I've tried a few things here and there.. But no real pharm experience. Oh, well actually, not quite true - I've got fairly strong experience with methadone and bupe.. By the time I started using heroin, I'd already been IV'n speed/meth for a long time and I wasted no time with lighter opiates, or smoking/snorting. So my only real experience with opiates is IV heroin.
I'm sure other opiates have very similar addiction patterns.. especially if you begin IV'n them. I know even taken orally/SL methadone/bupe are incredibly addictive and difficult to get off.