It's just frustrating to get incredibly good with shock, and then have to deal with other weapons. Shock can be one of the most technically interesting and skilled weapons you can use, because it's so psychological. You'll get into duels and be dodging around; you'll fire secondaries to make people subconsciously move away from them for fear of a combo, only to fall into your trap; you'll try to get a primary off to wear them down; you'll set up moving combos and get incredible shots that surprise and delight; and you'll fluidly move and get people right where you want them. It's also versatile for long-range shooting with good aim; I would always enjoy picking off snipers across the map on Face while flagging.
It can get so fun to develop skill in shock that you will get annoyed when other people don't use it. I often wish very much that there were still a good 1v1 shock mutator server out there. Nothing compares to shock on shock in the hands of two masters. Most other weapons are straight-shooting, like sniper, but shock rifle gets into high-level skill, manipulation, reading the enemy...it's truly a duel of wills and skills.
So, develop it for the sheer fun, yeah. But be prepared for the annoyance when you want to engage someone with shock, but they simply pull out sniper and get a headshot. If only they knew how fun it could be...
(And be prepared to be sad that shock is so nerfed in UT2K4 and UT3...)
If you want some real fun, pop into DoG Assault and play AS-HiSpeed, and get into some good shock duels on the roof of the train. It's fun to set up absolute domination on top when you're playing defense, and the narrow train roofs mean that any combo in the middle can be fatal.