Playing with irrlicht in C++ and TV3D in C# at equal amounts I think its fair that I compare and review them.
Firstly TV3D: When I started with this I had followed a few tutorials from C# for dummies and thought I'd implement TV3D and see what I could come up with, finding difficulties, as I didn't understand fully what to do, but I got around it, after getting my head around a simple text command I built upon that and got a little something I was proud of. I find I get a good FPS and uses Direct X 9 quite well and working with Dark Basic beforehand I picked up upon the similarities which became and advantage, however, to me it still seemed like Dark Basic, but harder, as the way in which it worked, it felt very much like after learning queen's english all my life then suddenly moving to Somerset, everything is said there and in the same way, but a change in words and other features. However, unlike DB it provided knowledge for the C-like structure and working a game engine inside of a main language, rather than cut down basic command. One disappointment is that we're still waiting for a public release of the new version, as for people like me I'll only buy an engine if I'm going to make use of it that exceeds the demo, its a turn down and the other would be the tutorials, at the time of starting I think there could have been better tutorial support for me, I don't think the comments in a source code is as efficient in teaching as they could be. Nevertheless its a great and power and cheap Direct X engine, I'd recommend to people who like to use .NET applications and Direct X. But me, its another stepping stone in learning to program games.
Irrlicht:
The first things that initially attracted me in one of it's mid BETA's (0.5 I think) was Mac capability with Open GL and the price tag (free), but then I didn't understand what the Hello World C++ tutorial means, let alone the Irrlicht, after coming from Truevision I though I'd give it another shot to find it at version 1.1 with more ability to use shaders and a lot of bug fixes, basically to me taking the next step at gaming gradually rather than chunks, which already graphically is capable. I find learning it very easy, the tutorials makes things oh-so-simple, so much I feel more of a geek thinking its easy, although no further experience in C++ other than hello world console commands, but previous knowledge in C#, the tutorials there are helping me understand how that works too. With the addition of irrlicht.NET, its open source community (such as open source games) and its new level editor, I think it could potentially increase its userbase quite well, which for those who want to use more that Direct X have the easier choice in programming. But in all honesty, I would have stuck with Truevision more if I wasn't going to go Mac, so those who are interested in using the Direct X API would benefit more with Truevision in my opinion and Irrlicht for those more Open GL and hate the interface of Visual Studio and the price of boreland products and like DevC++

I didn't mention anything about flexibility and speed and such like, but rather capabilities, understanding, as to me as long as there isn't a major difference in that, your ability to create a good game doesn't face a large difference between the two.