Gantz, Minimum Recommendations
Both MC's get thrown into a death game. Minimum has not been serialized for as long and is just starting to get more into the fighting rather than the nudity which it capitalized on in the earlier chapters. If you enjoyed Gantz you will probably enjoy Minimum since the targeted demographics are exactly the same.
Both series are very creative and when I started Minimum I felt a great kinship to the works of hiroya oku. I dont joke both mangakas have a very similar and beautiful drawing.