Solution to 3D has been deliberately left unsolved and is to be answered only by a non-regular / novice commenter, with proper annotation. Those who have answered earlier in the week, please give others a chance.
ACROSS
1 Murmur, “Russian tour’s extraordinary” (11) SUSURRATION*
11 I’m a creator designing incineration facilities (10) CREMATORIA*
12 Cheese from buffet appreciated (4) FETA [T]
15 Give description about sex appeal? Sure! (8) DEFINITE {DEFIN{IT}E}
22 Knights consume eggs at 12 in daytime (4) NOON {N}{00}{N}
23 Rascals wrongly counsel about doctor before commencement of surgery (10) SCOUNDRELS {COUNSEL}* over {DR} then {Su...y}
26 Matriarch in a warehouse hides crockery (9) CHINAWARE [T]
27 Receive accountant’s intelligent solution excitedly, for starters, getting a pay-hike (5) RAISE Acrotic
28 Bosses lost small purse containing six gold shillings (11) SUPERVISORS {S+PURSE}* over {VI} and {OR}{S}
DOWN
1 Wrongly takes some seafood (5) SKATE*
3 To some extent, retired hotelier was highly attractive (3,3) R?D ?O? (Addendum - RED HOT [T] - See comments)
5 Land surrounded by water mentioned in Haji’s letter (4) ISLE [T]
6 Repairs ruins including North, North Eastern and Eastern convents (9) NUNNERIES {RUINS}* over {N}{NE} and {E}
7 Indian revolutionary’s after a pop (6) APACHE {CHE}<=>{A}{PA}
8 Get away from Spain’s promontory (6) ESCAPE {ES}{CAPE}
14 Ivan chose flying fish (9) ANCHOVIES*
17 Threaten top pilot going after soldiers (6) MENACE {ACE}<=>{MEN}
18 English chapter’s first lesson on radio is unencrypted (7) ENCLAIR {EN}{C}{Le...n}{AIR} Enu should have been (2,5)
20 Elephant trek arranged around America (6) TUSKER {T{US}KER*}
21 Mike leaves go-getter with some ivory and bones (6) HUMERI {HUmMER}{Iv..y}
24 Knots ties around cross and leaves (5) EXITS {E{X}ITS*}
25 Initially park behind vehicle and crib (4) CARP {Park}<=>{CAR}
Reference List
New = N, Sex appeal = IT, King = K, Knight = N, Small = S, Shilling = S, Spain = ES, English = EN, Chapter = C, Mike = M