I like the features like floating with your angel wings, use your pet as a shield or charge it for special attack. The resolution is a little bit better than the resolution of the Metal Slug series.
The animations of the characters are much better in Metal Slug, more jokes, more different characters (mostly).
The sound effects of the guns are "heavier" in Metal Slug than in Demon Front. The shotgun isn´t that "powerful" when you pull the trigger in Demon Front like it is in Metal Slug.
The BGM in Metal Slug is much better, too. You´ll recognize it, when you hear it again. The Demon Fron BGMs are not very catchy - unfortunately.
Don´t get me wrong. I like Demon Front because of the side-scroll-run-n-gun-gameplay, but in Metal Slug you get more for your money. You will see it, when you can compare it directly.
I paid 250 Bucks for DF plus a lot of taxes - unfortunately. And I had to wait a lot of time for shipping from the USA.
Metal Slug X Kit costs me 70 EUR.
Of course not everybody owns Demon Front, but it´s not worth it just for storing it on your shelf - that´s for sure!
If I had the choice again, I probably wouldn´t buy it again for that price.
I just can say: blast away, and go, go, go!!! ^_^
MarcoRossi