Difficulty is highly relative the person playing obviously. Compared to most of what's out there though, especially the Japanese stuff, the game is fairly easy currently (though if you want it to be easier, remember that the clips are removable). It is indeed mostly a matter of swapping between the normal attack and the special, with an occasional re-up of energy, and unless you get unlucky with RNG the hardest part should mostly just be the slowness of wading through the encounters and making sure you don't waste items.
And I hate to be harsh, but avoiding combat is absolutely a valid and intended strategy here. It's a trade-off: You cover ground faster if you succeed, but if you fail you'll probably get swarmed and have to deal with several encounters back-to-back. So you can cautiously snipe everyone, or just open up a window and run through, the choice is up to the player. It's certainly not a serious stealth game with hiding mechanics and all that, but the enemies are actual sprites rather than random tile encounters for a reason.