For me the lack of proper music - either in the titles or the battles - made it feel a bit flat. The original theme did the job and certainly built up the atmosphere. Also I used to really enjoy the obstacle course in the early years - they dropped it fairly quickly so I guess I was in a minority but it made the show feel a bit repetitive with just fight after fight after fight, certainly when stretched out to an hour.
Yes! I enjoyed the first two series of Robot Wars, when it was half an hour - in a watch-it-while-having-your-tea way - but when it became 45 minutes in series three, as you say they dropped all the varied rounds and it became just a series of repetitive fights, and I more or less stopped bothering with it. But the show was at the height of its powers in that format, so seemingly it was only you and I who found it worse.
It sounds a bit odd to say it now, and I can't imagine what today's teenagers make of it, but both the Tuesday and Friday 6pm slots on BBC2 used to be required viewing, post-DEF II, the Tuesday slot featuring the Fresh Prince, Heartbreak High and a show I always enjoyed, The O Zone. In those days it seemed quite radical to have ninety minutes aimed at younger audiences. A bit like how the Friday night comedy on BBC2 in the nineties seemed exciting - THREE comedy shows back to back! And after the 6pm shows on Friday, over to BBC1 for Top of the Pops (I know Pops should never have moved to Friday, but it fitted into my schedule alright at that point, got rather stranded in later years when it was still there on its own).
The slot it has now, of course, is the one it had when it moved to Channel Five - for about three weeks, before C5 decided it was rating too badly and moved it to Saturday nights. And then after another month or so, to Sunday afternoons, and then finally to Saturday lunchtimes. It was suggested at the time that the mistake they made was simply making it a straight continuation, not bothering to try and broaden its appeal or work out why its audience was declining to the point the Beeb had dropped it.