It's interesting to compare their pre-Pepper UK singles with the US singles.
The US singles often included ballads and mid-tempo pop, e.g. "Yesterday," "And I Love Her," "Eight Days a Week."
The UK singles, on the other hand, typically featured harder pop-rockers, usually based on heavy riffs, e.g. "I Feel Fine," "Ticket to Ride," "Day Tripper," "Paperback Writer." These were all singles in the US, of course, but the US released so many additional singles.
These singles are all much harder and more powerful in mono, too. IMHO.