Something I'd really find interesting in the 5th game (if ya do one) would be a free play mode, with all the different tools from all the games and no objective. It'd be cool to see what players can come up with. Going over the top, people could share their own creations to see if other players can replicate them, user created level style. Might be a bit difficult to fit all those awesome tools on one page though. Ideas aside, thanks for 5 awesome Factory Balls games! I actually just finished replaying them in order. You have my vote for best puzzle game!
It's nice to see something like this; an game that takes an overused genre and mixes it up enough to be something truly new and inventive. I love the upgrades system and the step away from using "cash" or another single resource to buy things, and ground travel is a nice addition. My one and only issue is with the birds; they spawn exactly at my altitude, and at regular intervals, so I have to keep moving up and down. Oh, and the BGM is great!
Awesome concept, great implementation; putting so many aspects together and having it all work so well in the end. One thing that would help, IMO, is a comparison between equipment in your inventory and items you have equipped, as you hover over them, so that you don't have to go back and forth between the two. Even just having your equipped items also pop up windows when you hover over unequipped ones of that type would do it.
Before anything else, I love this game; it's clean, colorful, challenging, and above all: FUN, but I've been seeing a lot of cool ideas for how to make characters different, so here's mine: Each Ninja has a different ability that fills the Shadow Cloak slot, leaving Kenji with Shadow Cloak. Example: Shiro could summon a random scroll. Anyway, just joining the creative frenzy.
 "Factory Balls 4"){kind=icon}
 "Chuck the Sheep"){kind=icon}
 "Glissaria"){kind=icon}
 "Ninja Slash"){kind=icon}
 "Upgrade Complete 2"){kind=icon}
 "Pinata Hunter"){kind=icon}
 "Deep Sleep"){kind=icon}