The graphics are the same because the game is the same X_X but the new units look infinitely better than RTW units. Faction coloring (like Germans purple, Egyptians yellow, Seleucids gray) is not paid attention to to the point as in RTW where a unit is pretty much a big red man or a big green man or w/e.
The Roman units are much more colorful and interesting (Hastati, Principes, Triarii) along with the Italian auxiliary (Italian Swordsmen, Italian Spearmen, Italian Skirmishers, Samnite Mercenaries) and the mercenaries aren't all the same gay green shade--they have their own distinct colors that make them unique.
You can have your original RTW and play RTR too, provided you have enough space on your computer to install two different Rome Total War's on your comp. In which case, you have to re-name your Rome Total War folder, then create a new Rome - Total War folder, then put in the CDs and "uninstall" RTW, then reinstall it, and install the RTR patch over the new Rome Total War installation. Then you can rename that Rome - Total Realism or w/e and rename your old folder Rome - Total War (so your shortcuts can all work)
I have both my highly modded up Rome Total War, plus my highly modded Rome Total Realism, plus a whole new one I added yesterday to play Europa Barbarorum