A waaaay overlooked engine is NeoAxis. Which is open source and although GG has a far better community and the software is made by one man (same with NeoAxis), the ability to create a game in GG with amazing performance and graphics just isn't in scope right now. Performance is a major issue. Don't target lower PCs, it's not 2008. Obviously through MAJOR optimization in a game made in GG you can get decent visuals but let me show you a comparison. But still, even if you optimize, you need a beefee PC for a GG game.
1. I have a project in Unity which is an open world game, when you get into "zones" it loads and unloads entities to save memory. This game runs at minumum 45fps on my PC. There must be 600+ trees in the map. loading and unloading as you go.
2. In GG, an attempt to create the same map leaves me having to load new levels to compensate for the lack of performance. So you get to a point load the level and it still runs at 20+ FPS. AND my specs aren't bad. AMD 9290X, 8Gb ram, i7.
Sorry to sound like a knob, but get DX11 integrated and leave the OLD hardware behind.
@Lee, PLEASE look at NeoAxis and see what that guy has done. It really is worth your time for a bit of inspection.
Landman