Unreal 1: Obvious, huge, generous amounts of love in their labor. They really threw their hearts and souls into and it showed. The game was so popular that it spawned Unreal Tournament, which many would argue was a good thing.
Unreal 2: <the following is fiction, but it sure feels like the truth>
“Well guys we’re making Unreal Tournament 2003, so I guess, sigh, we’ll have to put out Unreal 2.”
“Awww… really? More work?”
“Hey, can we make it look like Halo and use marines and stuff like Halo? I really liked Halo.”
“This is Unreal. This isn’t Halo.”
“Yeah, but we could make it like Halo. Halo was successful. Let’s make it like Halo.”
“Well there would still have to be Skaarj…”
“Hurray! We’re gonna make a Halo game!”
“??”
“I mean, um, Unreal 2.”
“Hey, can we use the same map parts like they did in Halo? That probably took a lot of work out of it for them.”
“No, but we just won’t work very hard at it. Whatever you make it will be accepted. If you want to make really good maps, then go ahead. If you are tired or just tired of working, then that’s okay too.”
“Can we just make a side-scroller?”
“Let’s repackage Duke Nukem. No one will know.”
“Yeah, gamers are stupid. They bought Warcrap 3 you know.”