I really like HL2, and I do think you are over criticising the source engine. It is a FANTASTIC engine at doing what it does, which is realistic, belivable environments. The shaders used are brilliant, and realistic looking. It is amazingly scalable. Really, I have had it run on a 1ghz with a GF2 card in it. And it STILL looked good! Proberbly some of this can be atributed to HL2s level designers, though. Another thing Source has got going for it is the character animation. The engine has REALLY good lip synching and emotive animations. This I know is not due to designers, as Vampires: The masquareade: Bloodlines had very good animations too. And the levels are kept small because the textures, including shaders, are quite large, and they need to keep loading times down for slower PCs. Proof that the engine can handle large areas comes in the form of the Air boat and Buggy levels. These are large. Really large! Also the engine is modular, so it is quite easy to add completly new things in, such as the HDR in lost cost, or the up and coming next gen lighting render in HL2Ep2, which betters Doom 3s lighting and shadows.
The UT engine is a FANTASTIC engine though. It has support for a massive range of effects, has an easy to use map editor (not as flexible as hammer though) . The problem is, I am not sure in games powered by the UT engine how much of it is down to the engine, and how much is down to the developers. For instance, in Splinter Cell 3, a UT powered game, you have (propper) HDR, amazing shadows, great bump mapping, and also very nice sound effects (echoes, sound leaking through thin walls) but then you can look at say... Red Orchestra, where to be honest, it is VERY basic. Not a shader effect to be seen, very nice textures though. I think UT is more scalable than Source, but not by much.
The doom 3 engine, while having nearly every shader effect under the sun, including some REALLY clever ones, such as paralex mapping, which makes 2d surfaces look 3d, so when you move around them, what you see changes. Unfortunatly a downside of all these shaders is that it has the inherant effect of making everything look plasticy, , and having too dark shadows. This is proberbly because they act real, but the game does not factor the fact that real light bounces off things, it is why if you are in a room with one light source, you can still see stuff that your shadow lands on. It also eats ATI cards for breakfast, due to it being Open GL based, which the ATI drivers have problems on. It seems to be quite scalable, with tweaks, but not in game. (People have got doom 3 running on a voodoo 3, iirc)
I have not used Doom 3s editor, so I cannot comment on it.
