You're Minque's son? Nice to meet ya. Heh, maybe we can get your whole family on this board. That would be groovy, like a family reunion of sorts.
Anyway, to the matter at hand.
I have played Arena, Daggerfall and what I call Morrowind Lite. I'll give my opinions on all.
Arena: Rather bland, no guilds, utterly random terrain, towns way too large and horrible dungeons. One other bad point is the constant spawning in dungeons. I honestly can't count the times I cleared out a corridor, only to have a mage spawn two steps behind me and remove half my health with a single fireball.
But, Arena was the first and should be considered in its own merits. It wasn't too bad and it did brought us the most badass Battlemage ever to walk on Nirn. Jagar Tharn!

While the main quest is pure fetch and runs into a routine you can practically dream in no time, it does work simply because of Tharn's taunts. He's just creepy, the way he can find you no matter where you hide. The fact that you're basically tracing his steps helps him, but still. The guy can invade your dreams from the other side of the continent. Except for a Daedra and a dead spirit, that makes him the only person so far who can do that. And the way he replaces all the guards with shapeshifting demons, badass.
One other good point is atmosphere. While the constant spawning sucks, it does mean you are constantly on guard and you feel really tense, no matter how powerful your character might be. So yeah, Arena has its good points. It is the origin of TES and the origin of Tharn, so I like it.
Daggerfall: The second one. Daggerfall plays as an Arena MK II. It adds guilds, better character creation, background generation (pretty damn cool), an insane amount of clothes to wear (or you could go naked, if that's your thing), more weapon types (including flails!), more monsters, no more constant spawning in dungeons and so much more! Towns are still bigger than Vivec by the way, but the map has been improved there. At least you can now identify places of interest without asking everyone for directions.
Also, wagons! One extra uberlarge inventory? Worth every coin.
Downsides, the main quest is a bit disjointed. I've gone through the first one, but I don't know how to proceed. Somewhere in the entire bloody province, somewhere in one of the thousand towns, is the questgiver I need.
Other downsides, dungeons are even worse now. No more passwall, it's a 3-d maze that makes navigation a total nightmare. The fact that nearly all guild quests have you run through a dungeon doesn't help much. Then there are the time-limits on quests. While it is realistic, it does get on your nerves if combined with the dungeons. Also, outside terrain is still rather boring.
Morrowind: Morrowind took everything learned from Daggerfall and Arena, resulting in the following.
No more randomly generated dungeons, handcrafted quests (although a lot of them are still fetch), spears, crossbows handcrafted terrain (big point! finally real mountains!) and cities that are easy to navigate even without a map.
The only downsides I can think of are: No more flails (those babies are cool, don't know why.), no more wagons (or horses), no more climbing (well, there are ways even without levitation, but it is a lot less convenient) and less clothes to choose from.
Also, I consider the new slashing system to be more awkward. Unless you choose 'best attack only', you need to sidestep and stuff to make different moves. In daggerfall and Arena you just sweeped the cursor across the screen in a different way. It probably has something to do with the fact that you now can look in all 3 dimensions easily. Looking at the two, I consider ease of camera-movement more important than ease of doing a horizontal slash.
Favourite? Morrowind. While smaller than Daggerfall, everything it sacrifices are small things. Everything it gains are big things.
PS: Daggerfall works with Dosbox. I don't know how I did it though, I only remember it took me months of trying. Even now, movies and sound still doesn't work.