That's right, now even you can check yourself how unplayable Ultima IV is with the fancy Flash version, without fiddling with DosBox or setting up the Sega Master System emulator. It's free, allows you to save your progress (although I don't know yet how to transfer save files between different systems) and contains many improvements (the following is a selection):

• Dropped chests have four different levels according to monster difficulty. Thus there's more incentive to take down Gazers or Balrons versus Giant Rats.
• Random world monsters are specified by region, so you are more likely to encounter undead in the Fens of the Dead, or Pirates in the vicinity of Buccaneer's Den.
• Ultima V style reagent mixing. Specify how many cures you want to make, enter the reagents, and then be told if you were successful or not. 
• Ultima V style camping. Specify how may hours you want to sleep and who would like to stand guard. 
• See monsters, chests, and transports on view spells or peer gems. 
• Resize the browser window to play in full-screen mode. 
• Removed sleep exploit to remove poison.
• To be able to search for objects, players need to talk to people first. You can't just wander into Lord British's castle and search in the treasure room.
• Multiple keywords can be used to trigger conversation topics: e.g. you can ask about black or stone at the Britain pub. 
• Different cursors let players know when there is more pages of text to be read in a conversation response.
• Game contains online links to the complete PDF versions of the Ultima IV manuals and documentation, beautifully scanned from the original game. 
• Game has different combat animations to differentiate between attacks of poison, sleep, electricity, and flame.
• The original game data has been completely transferred into XML making the game almost completely data driven. 

Looks very well done to me. Go here, lose yourself in the world of Britannia, and be sure to contrast your experience with that of these fine gentlemen in the comments.
 
The new version is courtesy of ΦΨ software. I hope we hear more from them soon!