The thing I like about Line 1 is that even though each station has a relatively unique designs, there are clear demarcations in the architectural styling for each extension of the line. It should be obvious to observant riders that the Yonge subway (King - Eglinton), Yonge north (Eglinton - Finch), University (St. Andrew to Museum), Spadina (Spadina to Warden), Downsview and now Union were designed/built by different people at different times.
Since all of Line 2 was deigned and built at one time, we don't get the same effect on that line. Instead we're left with a rather drab and monolithic design. It also doesn't help that west of Victoria Park, Line 2 is almost 100% buried. This gives passengers who are travelling longer distances few opportunities to experience natural light, which doesn't help with the mood of the riders. Ever notice how passengers tend to perk up when crossing the Prince Edward Viaduct?
Thankfully the TTC has gone out of their way to avoid the mistakes of Line 2 with TYSSE, by ensuring stations have prominent natural light at platform level and unique station designs.