A Geometry Wars clone to learn the MonoGame framework and C# in general following the tutorial: https://gamedevelopment.tutsplus.com/tutorials/make-a-neon-vector-shooter-in-xna-basic-gameplay--gamedev-9859
There is a bug in MonoGame that results in the game waiting for the mouse to stop moving before updating the keyboard input which slows down the whole game in UWP projects. This has been fixed in 3.6.1 of MonoGame but the project is currently using 3.6.
once the enemy spawner class has been created, and implemented into the update loop we will gain access to the gametime object where we can implement this fix
Just for the sake of good practice, consider destroying any entity objects that have and IsExpired of true rather than leaving it to the C# run time to handle.