Revelation does have any new or unique theology to it that I'm aware. In that sense removing it would change little about the Bible.
On the other hand, Revelation brings closure to dozens of themes and motifs that run through all of Scripture, even from Genesis, so removing Revelation takes away this "bookend" that ties it all together and helps it all make sense.
Revelation helps us understand...
- the resolution to the problem of sin (the Eden problem) that started in Genesis 3
- the resolution to the problem of God being false construed that was emphasized in Genesis 11 (the Babel problem).
- the final resolution of God's presence that was lost in Eden, that was mitigated by the Tabernacle and Temple, that was exemplified and literalized in the coming of Jesus, and that is made complete in Revelation
- the final resolution of the covenant, started in Genesis 3, emphasized about 7 times through the Bible (Adam, Noah, Abraham, Moses, David, Jesus).
- the final resolution of the Temple, started in Genesis 1 (a temple text), continued in the Solomonic temple, exemplified and literalized in Jesus, and made complete in Revelation.
- the final resolution of the righteousness and holiness of God in judgment of all sin.
- The final resolution of how Jesus's sacrifice truly conquers death.
... and I'm sure there are many more. In this sense Revelation is a worthy book to include. It was also written at a time when Christians were being persecuted and killed, so it is a book of encouragement when the going gets really tough. Even though Christianity might not change much if you took Revelation away, it's an important book to leave in place at the end of Scripture.