No problem, Eldritch Horror is fine played solo with four Investigators.
It's really not that complex, though. There's only seven actions you can take even with the expansions (Rest, Shop, Prepare, Travel, Focus, Trade, and component actions), two of them can't be taken in an area with a monster, and every goal is "go here and do X". If you like it, make sure to get the Forsaken Lore expansion - without it the GOOs will become very samey very quickly.
Had to put the final push of Charterstone on hold for a week as someone couldn't make it. Instead we played London 2E (very good tableau builder), Barenpark, and Master of Orion: The Board Game (which doesn't have a board, it's another tableau builder).