None of the engines mentioned here can acomplish an equivalent to Doom3 at least not without investing a massive amount of time and labour - When you look at/play Doom3 the its easy to overlook how long and how great a volume of resources such a game took to put together. e.g. 25,000 textures alone so I believe.

The Reality Factory cell division demo uses textures cleverly and obviously painstakingly created (well done Pickles) to achieve the Doom like feel. Nice intro video too.

All of these engines have some good points and some bad ones which make none of them particularly helpful to indie developers who need an all round engine with a complete set of "basic" game requirement features (as well as any more advanced ones included) capable of rapid development to produce a reasonably saleable end product in a reasonable amount of time - that is unless you just want to make something for fun - which is admirable too of course.

AMP2 for instance has no terrain support.

Reality Factory does have a full compliment of features offering the ability to provide both indoor and outdoor (terrain) environments (as does both GS and Torque). RF also has an excellent feature set e.g. weapons, AI (not GS or Torque), special effects and more and rightly said it has an excellent top notch forum, perhaps the best - meaning its full of helpful people. RF I am not convinced offers high enough frame rates to consider making a modern game development with - (the complex environments that may accompany such a production), though the new release, currently in beta may well enhance this.

If your game design dictates smallish levels (cleverly designed) with a limited complexity, short range of sight and fogging your outdoor levels then RF may well offer you the nearest thing to a complete indie game system.

Most of the engines are undergoing development which promises us more and better in the future but for that day we shall have to wait and see - it may or may not ever happen.

Whichever engine here spoken of you aint gonna make a Doom3 or i'll eat my hat.

:-) maybe I will