Back to the question. iTech 4 is pretty complex. Its networking model is faulty for lower end bandwidth connection, however, we just tested deathmatch 1x1 on German server with pings ~160 and ~130. There was slight delay when damage is applied, however, for recreational gameplay it's totally fine (next week we'll test coop and that will answer many questions about idTech 4 networking performance in 2012). Hardware requirements were harsh by 2004 standards. The engine was (and is, in some respect) ahead of its time. UE4 is bringing in 2013 (or whenever released) sort of unified lighting with soft shadows and real-time GI, but last time I checked it was running on PC that virtually no one owns. So for most gamers it will be lightmaps with few real-time lights, just like in UE3 (there are a lot of other improvements of course, but I am comparing lighting). Unreal Engine offered artists friendly tools, least to say. Have you tried DoomRadiant? I think there is no way to switch projections in DoomRadiant (unlike GTKRadiant / DarkRadiant) - it's top view + Z-window and it's beyond me who came up with such a bad UI design. There was only Maya plugin to export models. So you had to had LightWave + Maya to get content into your game, while UnrealEngine supported Maya + Max and required no mess with manually editing game filed to specify proper materials/sounds/etc. Apparently support from Epic was better than support from ID. Having middleware that adds features to the engine and doing better job than idTech 4 in some cases helped too. To top it all off, UE3 ran on consoles, idTech 4 required third party developers to develop ports (and Xbox only at the time).
So here you have awesome ahead-of-its-time engine, with poor support, poor tools, high hardware requirements and bad networking (high speed broadband was not widely available back then) and no in-house console port; and you have also good looking engine, not whole a lot innovations, but with good support, console ports (including PS3, which was not supported for a long time by idTech 4, if ever), awesome tools, very robust networking, very scalable allowing it to run on older hardware. In other words, you can get job done faster, in artist friendly manner, get help when needed (after all, engine licensing is a huge part of Epic's business and they have dedicated people for support), release your game on PC + consoles, etc. So no matter how fan you are of new tech and idSoftware, when it came to earning money it was a no-brainer choice - go Epic.
So it's not that engine was bad or Doom 3 was bad (Doom 3 was an awesome game, and as some one mentioned it, it was highly praised by the press when it was fist shown), it was about business model. That's the reason idTech 4 was not licensed by as many developers as UnrealEngine was. Note that lack of Linux/Mac support never stopping Epic. Go figure. Perhaps most gamers do have dual boot after all
IMO Rage is an outstanding game. I didn't even care for non-interactivity (can't shoot lights, can't shoot cans, etc.; all idSoftware games were the same way before Doom 3). Rage is beautiful, atmospheric, drawing in. It has it's cons, the biggest of which totally flawed ending (it would be good if DLC or expansion was released soon after).
The issue with press is that people who should stay away from reviewing FPS games, do that anyway because they have no choice. Or they hate those games so much and they have an opportunity to work overtime to spit on those games, which they use at maximum. So if I don't like 2D 8bit looking games, and I have to review them, I would most likely express personal opinion about it and a game like that will get 1/10 score. However, that's not how professional has to do it. It has to be objective review taking into consideration "what would average FPS player / 2D 8bit-lover player feel and think about this game". Talking about Rage, virtually all negative-to-the-core review made as personal vendetta on idSoftware as if the reviewer wanted good old FPS and got broad modern atmospheric FPS instead (if it would have gameplay as Quake, for example, then it would count as repetitive shooter for trigger happy old timers; that's just how it goes nowadays, or so it seems; none of the jornos seem to be happy).