I'm with charbydis on this - Linghu Chong wasn't well done at all, but the rest of the solid TVB 80s veteran cast gave great performances worth of their pedigree and made the show watchable, even enjoyable if you were a 14-year old who didn't read the novels. I recall gleefully figuring out which laser bolt came from which character, and prided myself on knowing what what art each character used and the colour of the beams and sound effects.
Kenneth Chang was probably the best Yue Buqun I have seen (but then again any role he touches, with the exception of Xie Xun which imo Shek Kin was more natural in portraying, is hard to beat). Yeung Chak Lam's Zuo Lengchan was suitably sly, cunning and dangerous, while Lau Siu Ming's Ren Woxing was just top class. Simon Yam's Liu Zhengfeng and Kam Kok Wai's Qu Yang were both very likeable, while Fang Zheng was probably Pak Man Piew's best ever Jin Yong role. Even though we all laughed at Kong Ngai (I can't imagine anyone keeping a straight face when he goes "hai mm hai Yam Ngor Hang arr?" and turns round to face the screen) he did look very very scary and villanous (and I thought his Wolverine hairdo was quite cool). Lok Ying Kwan in those days still did lesser roles (which kind of suit him more) and his Yu Changhai was really well done. Even Kwan Hoi San and Nam Hung's small cameos as Mr and Mrs Lin Zhennan were really memorable. Ko Hung never got really good roles in TVB, yet his Mo Da was pretty cool, while the three Ding nuns, led by So Hang Suen, didn't really put a foot wrong (although I can't remember who played Ding Yi).. and so on. Look out for cameos by Lawrence Ng, Kiki Sheung (as the ill-fated children of Liu Zhengfeng), Francis Ng, Lau Ching Wan, Eddie Kwan too! With kelefes like that, it must have been a strong cast. =)
The themesong was also great, among the greatest of the golden 80s - probably only the LOCH duets and the Flying Fox duet give that same feel.
Granted, Linghu Chong lacked charisma, and so did Tung Wai as Lin Pingzhi. The girls acquitted themselves well, though, and Rebecca Chan and Jamie Chik were both very likeable. Wong Man Yee was pretty, but didn't seem to act the role that well. The plot changes were not great, and that Yue Buqun/Ren Woxing fight was just ill-advised (although when Zhang Jizhong did it in 2001 a lot of us approved). However, TVB always had a penchant in the 80s for doing things like this - dragging on a series by putting in extra boring drama - even LOCH and ROCH had no end of either soppy or unfunny humourous scenes.
In short, yes, having a weak lead kind of took the gloss of the production, and pretty much ruined it, really, but the rest of the cast were quite solid. There have been many serials where the lead wasn't brilliant but the supporting cast made the series (Snow is Red, Mythical Crane and Divine Needle etc), and if it wasn't in the middle of the golden 80s, I think it would have been judged more leniently.