I can rate this mod in a few ways, actually...
Gameplay = 6/10 : Initially the game is very engrossing, especially for fans of the series, since you want to see everything this mod has to offer. Sadly, you find it all relatively quickly, making the replay value considersbly low.
Graphics = 7/10 : The models and animations are above par in terms of raw detail and staying true to the series. Even the little things, like Vegita crossing his arms when standing idle, give the game that familiar touch.
Sound = 6/10 : There simply isn't enough of them and not at a very great variety. Of course the sounds they do have are quite good. Watch the transformations to see what I mean. It makes you want to break things.
Value = 7/10 : Excellent because the game is free (for those who own Half-Life of course) and is constantly updated. If this mod has any weakness, it's the lack of games modes and replay value. Luckily, this score is heightened due to the fact that these things will likely be fixed in the future.
Tilt = 7/10 : Compared to its competitors, ESF is a pretty sweet deal. It's made by the fans for the fans by people who didn't have to make it in the first place. Cudos to them for devoting their time and money to this project.
Overal = 6.6/10 : A good mod for the fans and a little something for everyone else too. Currently the gameplay is a little stale and needs some freshening up, but that will no doubt change once the mod launches itself out of its beta stages.