Sometimes it's easier to work with the expression in an APPLY block, dropping the results down to the WHERE clause like this:
SELECT e.*,
x.Datefilter,
x.LookupFilter
FROM tbl e
INNER JOIN LKUP L
ON e.ID = L.LKUP_ID
CROSS APPLY (
SELECT
Datefilter = CASE
WHEN YEAR(SU_DT) = 2014
OR MONTH(SU_DT) >= 11 THEN 1
ELSE 0 END,
LookupFilter = CASE
WHEN LKUP_VAL_EN LIKE 'V2%' THEN 1
WHEN LKUP_VAL_EN LIKE 'V3%' THEN 2
ELSE 0 END
) x
WHERE e.Active = 1
AND (
(x.Datefilter = 1 AND x.LookupFilter = 1)
OR (x.Datefilter = 0 AND x.LookupFilter = 2)
)
For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden