It should play Doom at about full speed - I recommend "Doom Attack", because it has extras features like a jump key, look up/down keys, etc. ADoom might be slightly faster on an 030.
AB3D is fantastic on an 030. The WHDLoad version of Stunt Car Racer with the turbo patch activated is also good fun. Other games are Breathless, Gloom, Hexen, Heretic and Legends of Valour. You can get F1GP to run faster if you use the editor from the Aminet.
You'll be able to play MP3s, albeit at low quality, with MPEGA from the Aminet. OctaMED Sound Studio will can take advantage of the faster CPU and extra memory in "mixing" mode, and play back longer samples and more tracks in 14-bits. Anything running from a hard disk will load faster, the computer will boot more quickly, Workbench won't be so sluggish, higher resolutions in DPaint become less frustrating to use, 3D applications will render faster, Wordworth 7 will run...
Oh, and don't forget the emulators. AmiMasterGear, AmiGameBoy and AmiMSX will all run at full-speed. DreAm (Dragon emu) will also run at 50fps, as will ZXAM (Speccy emu), CBSpeccy, Wzonka-Lad, A/NES (non-CGX version) and CoolNESs. PC-Task and PCx will be vaguely useful at emulating 4MHz PCs.