Defold is great! It is one of the best (most feature rich, most productive) game development option for 2D focused dev available today (and is making progress toward being great for 3D in the future too).
Cross platform - iOS, Android, Win / Mac / Linux / HTML5. 2D first class, but still supports 3D.
Light weight, super high performance, very highly optimized (works great on older, slower devices - for when you want as many people to be able to play your games as possible).
Many useful built in features such as signed distance field fonts, automatic texture atlas generation, automatic per-target texture compression, support for IAP billing for iOS/Android, support for delivering a smaller game binary and then streaming in extra content as needed.
Enables productivity and collaboration out of the box. Make changes, sync to server, and then your team members can pull to see the changes. References are updated as you move files around in the editor which cuts down on tedious work when refactoring.
Has great support from great devs. The Defold development team makes frequent updates, and is very supportive and active in the community.
Defold’s future is very bright, it has a growing community, and strong support from its developers who also have a strong desire to not break current projects with updates as the Defold engine and editor continues to evolve
Besides the technical reasons, there are other reasons which you should be aware of that should make Defold an appealing option. By working with Defold, there may be opportunities you may never be able to get using other similar tools - such as having a hiring advantage for companies using Defold. Learning Lua through Defold is also useful as many other game development tools also use Lua.