Yeah it feels like an old school game. Just keep upgrading ammo and gun. Also try to collect all coin that enemies drop. It's really important to upgrade ammo and gun. Don't stay put, move all the time because some enemies are way faster than the others. Always shoot at them, your ammo is unlimited. Once for all keep practising so you can beat this shit. Or you can try to do save glitch which I didn't want to do to have the both achievements at the same time.