In order to become a classic game, you need to not only do something new...but to pull it off well. RA2 brought in lightning-fast gameplay, tech buildings, and many units with game mechanics previously unseen. Generals brought in the generals point menu, added late-game resources and again...added a good deal of new units with game mechanics that weren't seen before.
The most important thing in an RTS is the units. Compare RA1 to RA2...RA2 brought in a ton of great new units (which had new gameplay mechanics);
Allied GI (deploying)
Chrono Legionaire
IFV
Prism Tank
Chrono Harvester
Yuri
Kirov
Terror Drone
War Miner
I only listed the most important ones...the fact is that in terms of unit design, it was lightyears beyond what was available in RA1 (which aside from a couple units was light tank, medium tank, etc. generic type units).
Just to be sure I am within bounds of the NDA...lets just look at the units listed on the RA3 website;
http://www.ea.com/redalert/factions.jspThe only unit there that I'd even consider listing (in terms of comparing RA2 to RA3) would be the Sickle...and that is something I'd consider boarderline.
Go read up on Starcraft 2...they have the highest percentage of new units, with great new mechanics of any RTS I've seen. This isn't surprising though, since its lead designer also designed RA2 and Generals.
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Now in regards to the other attendee's, lets keep something in mind
1) Its in their best interest to portray RA3 in a positive light. They run websites, forums, etc. and expect to have a future relationship with EA. MEC2 is my last mod, I have no plans on modding another C&C game...thus my perspective is different.
2) I also have a different look at the design since...I've spent the past year slaving away on an RTS of my own (MEC2), which takes heavy influence from past C&C's. I've studied the hell out of them, and most other major RTS's...and have a decent grasp at what makes one work. When I look at RA3, all I see are errors...things that should be tightened up (in the design).
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Now since this is the MEC2 forum, I should point out that seeing RA3 has had a positive influence on MEC2. Right after I typed up that 10 page document...I took a day, and redesigned half of the IDF's units. Prior, the IDF had great overal game mechanics (the mobility, trophy, etc.) but its units were fairly generic (deployable attack cycle, apc, generic tank, generic helicopter)...so that was corrected.
We are still working on exactly how it'll work...but the core idea for the Merkava's change is that it no longer has the medic-upgrade (that'll likely be shifted onto the APC), and that its death actually has two phases. Once the Merkava is knocked into phase 2...its essentially berserk, it'll move much faster and deal much more damage....however, it'll take constant self-damage (to its already weakened frame) until it finishes dying. This brings up new options for players, do you keep it alive with mechanic drones? Do you damage your own Merkava's to hit them into phase 2....in order to get a much improved hit-and-run force? and many more choices...
I'm following SC2s developement very closely, and so far, I have seen not much innovative or a great plethora of excellent units- It's ok, but RA3 does not have to hide from SC2 (Especially in the level design department, imho). But please do enlighten me. Because most of what I've seen, is fairly generic. Whilst co-op campaign or water bases aren't.
Let me elaborate:
Overlord: Elevates the cap as he previously did, blocks resources (Like destroying Tib), hurls creep (Adds space for building like a surveyor)
Baneling: Suicide unit (Just like the rolling bomb from Generals or the fanatics from TW)
Corruptor: Works like mind-controlling units (RA2, TW)
Drone: Gathers resources (Harvester)
Queen: Heals (Like the "Repair button in the sidebar) and poisons (Toxin tractor)
...and I could go on. But it's boring

Perhaps it's easier if you list me the innovative new elements of SC2.
The RA2 units you listed were- partially- intriguing, but their strategic depth of their abilities was reduced due to being passive abilities. Do tell me about the unit errors! I would not say though that the other atendees sugarcoated their experiences, judging from Hexetics UI and visual error write-ups, Sonic's general desinterest in RTS, and although JohnWEs a huge CnC fan, he's not without his share of criticism. Wildfire is the only one who might be a little forgiving with EA.
I'm on the opinion btw, that not units exclusively make a good RTS- It's also gameplay and diversity that counts, and on that front, RA3 seems to do much better as TW, and, if it turns out well, even RA2, due to the focus on one-purpose units with one secondary ability.
I'd like to showcast these units:
-Cryocopter: Both the freeze and shrink ray sound quite innovative due to their implementation- The shrink ray has advantages and disadvantages, so it's useful even for your own units, and the freeze ray is even able to freeze buildings.
-Peacekeeper: Their damage decreases with range. Sounds pretty new.
-Spy: Permanent control of xy units
-Riptide: Weapons change from land to water (The whole emphasis on water is quite innovative anyway)
-Century bomber: Transports any kind of infantry or carpetbombs- Pretty nifty
-Mirage tank: Mobile cloaking for friendly units
-Tanya: Teleportation combined with fully restored health
-Bullfrog: It's unloading method renders it quite fresh on it's own, but it's also a dedicated anit-air weapon, making it more useful then your basic transporter
-Terror drone: Stuns enemies, but does not disable their weapons
-Apocalypse tank: Grinds enemy tanks. Nuff said

-Hammer tank: Sucks life out of enemy units to steal their weaponry if he's able to finish them off
-Natasha: Is able to shoot 6 infantry units if they're in a line
...and I do not even know much of the Japanese yet!
So as you see, RA3 has it's own set of imaginative badass units as well, plus having RA2's IFV, Kirov, terror drone, and similar gameplay mechanics of Yuri, Allied GI and Chrono harvey.
Furthermore, it has much more diverse and detailed scenarios, which is a very important factor, walls (Unlike Generals or TW), General's eco+ support power system (tweaked), Frank Klepacki and three quite diverse sides, besides a co-op campaign, among other things.
I ask again: What's not to like?