Dune2 was first one that qualifies (and i will stick to this) *definition of RTS* - base building, resource gathering, producing units and direct control.
I had on SeGa mega drive2 - Dune2 (westwood), Mega lo Mania (sensible software) came out just some month later after dune, however this one was first rts to have tech tree, Bullfrog games (or more precisely Peter Molyneux's games) are like nothing else; i had Populous2: two tribes - technically not rts since no direct control over units, but damn, game is something, also theme park, but that one is definitely not rts.
Bullfrog made dungeon keeper - a game to remember for sure. Then there was KKnD krossfire - cnc clone by aussies Beam software (they also made stuff on sega md - platformer game 'Blades of Vengeance'). Also can remember 'Machines' (abysmal pathfinding), RA2 (doh), Emperor battle for dune (awesome soundtrack by David Arkenstone, even outdone Frank Klepacki on that one), GeneralsZH (EA) - good one, Sins of solar empire: rebellion (no idea, downloaded that one some years ago to check out, pretty decent, can't say much else), SupCom/FA (is good), SupCom2 is weird, World in conflict (from that video) - trash-y and not rts. Never played any of settlers series, but there is Widelands (that i discovered at the same time as zero-kelvin), can't say i got hooked, but game is sure worthy especially considering how much stuff is going on and how smoothly it runs even on +20 sim speed (also 'strategic zoom'(TM)) - that one caught my interest since i kinda like 'city building' games like Pharaoh and Caesar series (presumably by Sierra, but not sure, maybe they had different divisions) which are not exactly rts.
Probably RTS game that i played most is first Spellforce - RTS/RPG hybrid, i mean if they can fuse two genres and do it decent enough, why not (also after long time playing same game one inevitably might come to conclusion that some part is utterly broken, in this case RPG part is broken, but doesn't matter for single player). Looking at addons you can see quality decrease - flat maps and recolors all over the place, voice acting notoriously abysmal too. Second game is just blatant warcraft clone (firs one has vibes too, but still a very good game) and they got what they truly deserved for this - they gone bankrupt.
And i one of opinion that only good games from Blizzard are lost vikings and RRR, simply cannot digest their rts games; as well as those 'worldwar realisms simulators', you have virtual space where you can do literally anything you can imagine and what you do is try and port something representing 'real' stuff? That is definition of 'DULL'.
I would consider myself something of an 'rts enthusiast', however nowdays i don't follow any news, and there lot of stuff of category 'never played, never will, don't care in a slightest' (starcraft2 for example).[Spoiler]
On a side note: i would consider myself UT fan-player and in fact ut2k4 had rts mod, but if you make a wild guess and name a random feature, chances are that ut2k4 (ue2-2001-2006) already had it (2d shooter/platformer, rpg-pve/coop survival, sandbox basebuilding and many, many more), no wonder Epics got big nowdays.