Metal Slug 3 was and still is one of the best R&G game that ever existed, considering worthy to be the last installment in the MS original trilogy.
However, DOTEMU, did a horrible job porting this arcade gold to STEAM, as for now it's porly optimaizet. The bigest problem it's the UI constantly putting a fight against you. If you can get past those mind-raging controls then you got MS3, but since i love MS and you, i'd recomand to keep your coins for a better deal.