Unity is a multiplatform game development tool, designed from the start to ease creation. A fully integrated professional application, Unity just happens to contain the most powerful engine this side of a million dollars.
Honestly, the best engine I've worked with. It's amazingly simple but also amazingly powerful. It includes enough features in its free version to get you started on whatever project you might want to work on, and even get it to near completion before buying the pro license.
It understands my favorite programming language: C#. It uses my favorite framework: .NET. Chances are these are your favorite things too!
The editor is awesome, and it accepts tons of file formats for assets.
Add cross-platform compatibility to that, and you've got yourself a winner.
Well Unity3D is AWSOME!!! You can really do amazing stuff with it. The fact that you can add models from any 3D Modelling Program is actually vary cool ( ok it exists in other engines too but it is cool ). The only thing in my opinion doesn't work well is the build. Sometimes when i save a script it doesn't debugging it right away 0.o . But I'm sure that next versions of Unity3D will have it fixed because this guys are awsome!
the easiest and most user-friendly game engine currently out there. it has some of the best support and documentation, not to mention a great community where lots of questions are answered. the only negative is that the pricing for the pro version is a bit high for some individual programmers and devs, and i do wish they had a pricing plan where they gain a percentage of profits from the game and charge a small fee instead of charging an instant $1500.
Unity is a really great game engine. the editor is customizable with it's own scripting api. the pipeline is customizable too.
all features are easy to use and the engine can make small indie teams powerful groups to make huge games.
there are great add ons for most missing features and it's becomming as popular as techs like flash.
unity's asset store will allow developers to cooperate and use each others work with great prices.
there is not any other single engine with this price range with these features. if comparisons were allowed and tolerated, i could post advantages of it against all other engines this side of the market (i mean less than 500K dollars and without royaltees)