No emulator can fully recreate the arcade experience. Please patronize your local arcades to get full enjoyment from Metal Slug X. Even better, go out and buy a Neogeo and an MS-X cart.
Prices are quite low now, and are still dropping.
The good news is that SNK is still making games for the MVS system. The bad news is that they may just decide that it isn't profitable to do so anymore. Let's allow them to get the profit they so greatly deserve by not releasing new roms too early. By practicing self-moderation, the emulation community can show its detractors that emulation is not necessarily a bad thing.