I feel the same. I want to play the originals, but they are just so clunky and even the mods do not fix the fundamental problem of how old the games do feel.
The original DX, on the other hand - it took me years to get past the first level, but once I did it was really engaging.
Penny Arcade captured the sentiment at the time pretty well:
https://arewenewatthis.files.wordpress.com/2011/10/deus-ex1....
(Sorry this is not officially from their site--their archive search system is terrible)
The unavoidable boss-fights were certainly something of a shock at the time.