Look at Orcs Must Die 2

Part tower defense, part action RPG, orcs must die 2 is a compelling package at first, there are tons of traps, weapons and trinkets to collect and upgrade and there are also tons of level to try and perfect. After playing with it to completion, twice, my desire to play it again is greatly diminished for various reasons regarding map  and item systems design.

Right this way Mister Orc

With four spawn points and no
chokepoints, this map is not fun.

The maps in OMD2 are ranging from mines to castles to ice caves and lava-filled structures. All maps have spawn zones where enemies appear and rifts where enemies try to go and die. They did a great job of adding more environmental hasards this time around such as minecarts that roam maps, killing orcs for you, or chandeliers ready to fall on enemies. The maps never are simple; sometimes they have multiple levels and they also might have up to 4 doors where enemies come out of. Sometimes there are natural chokepoints where you can dump all your towers, but must of the time there aren't and you need to place them at multiple spots, this gets harder in single player where you have enemies coming out of two different ways most of the time. I love chokepoints in my tower defense games, making huge piles of towers on one spot is a great way to have silly, senseless fun.

Another thing I have against the map design in OMD2 is the fact that it doesnt allow the use of your favorite turrets. I really love most of the turrets that come out of the ceiling and some of the wall-based ones. It's really a frustrating experience when after level 3 or so, there is no spot anymore to place ceiling turrets. After a while the corridors become so wide that it's not really useful to place traps on the walls either! Floor traps and guardians (NPCs that either block the enemy's path or attack them from range) work pretty much everywhere, so they're the go-to in terms of versatility.

How I would fix that
A small amount of level design changes would fix my issues with the maps in OMD2. Add more chokepoints, lower the ceiling at places, tighten some hallways, funnel the path the enemies take... That seems like it would fix both this problem and part of my other one.

Swiss Army Traps Knife (Or how often do you use the corkscrew)
There are TONS of things to use for your character in OMD2. Almost 20 weapons, traps and trinkets, it's enormous. You can also upgrade them with skulls gained from beating levels under certain conditions such as not letting a single orc pass or finishing under a time period. The upgrades are interesting, most items have a general upgrade that you can purchase multiple times and increases a base stat for that item, such as attack or reducing cost. Most items have unique upgrades where you need to choose between two things. In theory this is a neat idea, in practice one of the choices is superior to the other no matter how you see things. For example, archers can either regenerate health or shoot fire arrows. Archers are fragile and can't take a hit, they really die in one or two attacks. The health regeneration is so slow that they still die all the same, while burning enemies with their attacks is great and adds a bit of crowd control (Because enemies on fire run around). Other items have special upgrades such as being able to place floor traps on the walls and the like.

Guess how many of these things I've used. Answer is not much, and there are two more pages of these things.

Weapons are varied and interesting, from a wand that shoots mind control bolts to a ring of polymorph, you can really select something that suits your playstyle. Except if you want to attack all the time. Or not have to click constantly. Or if you want to deal any kind of damage. I bought many weapons to try them out before realizing that most of them require mana to attack and will stop doing anything before your mana goes back up. Most weapons need you to click repeatedly to attack, I know it's a small thing but it gets tiresome after a while. The default attack for the sorceress's wand is really low so you kind have to spam charged shots. Trinkets are fine since they have passive effects (and an active one that you activate with mana). They would matter more if the game was about you killing all the orcs instead of your traps doing most of the job,

Archers are good but they go down really fast, fast enough that regenerating health wouldn't matter.

Another problem with this system is that there is zero incentive to try any of the weird stuff. I've beated the whole game with the default sorceress weapon, a trinket to regenerate guardian health, a trinket that increases the gold you make, archers and paladins. Never I lost and had to rethink my strategy to change things around and approach the enemies in a different way.

How I would fix this
This is not easy, but a way to give meaning to all items and traps is to give a reason to use them. What I would do is add another upgrade for all items that would be multi-level and would go up when you kill enemies with that item. To make it worth trying, this upgrade would improve items greatly such as removing mana costs or increasing damage in a significant way. Maybe tie-in achievements to specific weapon usage? Have some levels require you to use specific things to 5 skull the map? Upgrading your items to the maximum level could give you part of a golden key, when you get them all you unlock a special challenge map! Anything!