I have a couple isometric prototypes going, an RPG and an RTS. I haven't gotten enough done on the RTS to show it off yet, but here is a pic of the RPG.
The RPG prototype is tile based. I originally made it using an array to generate random levels, but later decided to place them manually for more control.
The bottom picture shows the grid system I built in Photoshop to easily place tiles that would lock into place on a grid in Construct 2. This took several hours to make. Basically, the first frame of the animation is the grid, and it changes to the actual ground image when the game starts. This produces less clutter in Construct 2, and enables fast placement of tiles.
I never finished this RPG prototype, so the character models are still Golden Axe placeholders!
I am currently working on the RTS because I think it will be easier. It doesn't need a grid since it will be on an open map with a tiled background. Everything will still be isometric though.
I am basically taking the approach of older games like Baldur's Gate with pre-rendered 3d images (made with Modo and Zbrush).
Unfortunately, Construct 2 does not have any built-in framework for isometric games, so you have to set up everything for isometric yourself.
Note that these two pictures are not of the exact same scene, so if you see tiles placed in the bottom image that don't make sense, just ignore them.