Empire Earth

In the Might and Magic Series, in my opinion 4,5(world of xeen) and 6 are the best. The Sequels are getting worse in my opinion and the earlier titles (1,2,3) are somehow restricted in the character development and the diversity of the world.

I guess nowadays its hard for a sequel to beat its precursor, because the expactations are kinda high. That was the case in Diablo III last year. It was nearly impossible for it to beat Diablo II.

Europa 1400: The Guild - Its sequel tried to be Sims instead of being economical sim.
Mafia
Fable

The first Age of Wonders is far better than Wizard's Throne and Shadow Magic put together. But that it, of course, my opinion which is kinda subjective

Original superior: Fallout, Tropico, Stronghold, STALKER

1)Betrayal at Krondor
2) Knights of the old republic 1 - arguably; since the KOTOR 2 patched with restored content is actually better than the original
3)Medal Of honor - IMO the original is the best one of the lot
4)Call of Juarez
5)Diablo -
6)Alone in the dark
7)Crysis
8)Far Cry
9)Duke Nuke 'em 3d
10)Fear

I find Might&Magic 1 and especially 2, to be vastly superior to MM3-5, mainly because I'm a "combatfag".
The Magic Candle.
Buck Rogers.
Deus Ex.

Aye, that be true! Antara was just not the same but the real horror came with Return to Krondor.

Desperados: Wanted Dead or Alive is another example. I would rather forget about Cooper's Revenge...

FEAR
Blood
Carnageddon
Dark Reign
Desperados
Sacred
Unreal
...

Discworld (The sequel might have a bit less obscure puzzles, but it didn't have as much charm as the first one, IMO).

Gabriel Knight (I mean the second one is fun in its own way, too, but the first was even better.)

Lands of Lore (The Throne of Chaos was perfect, the pinnacle of tile-based EOB-style dungeon crawlers, LOL2 tried to do something a little more modern, but it wasn't as great as the first one.)

Maybe, just maybe, Neverwinter Nights (Pretty subjective and bound to evoke controversies, since NWN2 improved on a lot of things, but sadly it also made other things worse; rather than just improving the predecessor, they almost made a different game out of it; personally, all in all I prefer the old one, but that's also due to my taste in graphics, the immense community work and NWN not requiring as many resources to play and probably less time and experience to build with; as far as the campaign and party handling is concerned NWN2 is definitely superior).

Deus Ex

Dark souls is very good game but I think itd much harder then demon souls because the world is bigger and you have more ways to go. Dont know if its more laggier but its the same system as demon souls you can invade and be invaded if you are in humn form.

Dragon Age Origins - I like DA2, but the 'press button make awesome happen' philosophy really hurt it in some areas.

X-com UFO Defense - all the true sequels (Terror From the Deep is a standalone expansion pack IMHO) focus on the setting not the gameplay. :/

Dead Space - RE4 style survival horror isn't mainstream enough so it had to become a TPS.

FEAR - the AI in the original puts on a good show. the sequels can't touch it.

Only game that comes to mind that's not been mentioned is BF 1942. I didn't like the direction DICE took in BF2 with ranking up for weapons or the removal of naval combat. The latter was understandable with the modern setting, but I miss bombarding the coasts with naval artillery, or maneuvering ships so the enemy couldn't take out our planes on carriers.