While the soapy era saw The Bill lose quite a lot of its soul as it became just another soap, it was very watchable and at times quite addictive. While some of the plots were incredibly implausible, they just kept you hooked. Like, as the poster above noted, the Sam/Abi/the profiler story, Gabriel Kent, Cathy Bradford, the Sun Hill serial killer, Chandler's fall from grace, the Sun Hill explosions (both of them), all just kept you gripped. But I can't really class the soapy era as proper Bill.
The proper Bill ended when Don Beech left with the rest of CID. Best eras for me - 1988-1993, dipped a bit when Burnside left but the show returned to form in 1995. 1995-1997 was solid, early 1998 was rubbish as they were burning off the last of the half-hour episodes though there were some solid efforts like "Villain" when Boyden talked with an old man in custody for the whole episode, "Square Peg Round Hole" when Boulton was stabbed with a needle, and "A Rainy Night in Sun Hill" with the conflict with Santini and Hollis. Then the hour-long episodes from late 1998-2000 were mostly excellent.