Various aspects of Lord Shiva are revealed under Rudra Suktas of RigVeda. They are like:
1) Revealing of Lord Rudra as One without Second:
Lord Rudra in Vedas has one peculiar characteristic ie. He is stated as the one without second. YajurVeda Taittariya Samhita 1.8.6 clearly states 'Eka Eva Rudro Na Dwitiya.' ie. 'Rudra yields noone to second.' Now a question arises whether this is just Arthavãda or has special significance. It is not Arthavãda because same verse is derived by Svetasvatara Upanishad in 3.1 and used as to glorify Brahman 'Eko hi Rudro Na Dwitiyaya... '. So, Lord Rudra is the one who is without second. Same thing is also revealed in Rudra Suktas of RigVeda:
न वा ओजीयो रुद्र त्वद् अस्ति
na vā ojīyo rudra tvad asti (RigVeda 2.33.10)
a mighter than you there is not Rudra.
अषाल्हाय सहमानाय वेधसे
aṣālhāya sahamānāya vedhase (RigVeda 7.46.1)
whom noone may overcome.
Mightiest of the mighty. (R.V. 2.33.3)
2) Revealing form of Lord Rudra:
The form of Lord Rudra is well revealed in YajurVeda. For instance YajurVeda records Lord as blue-necked one, rider of bull, holder of Pinaka, wearer of animal hide etc.. but still RigVeda also reveals some aspects about form and aura of Lord:
trayambakaṃ yajāmahe (RigVeda 7.59.12)
We worship the three eyed one.
kapardine (Rig Veda 1.114.1)
One who has matted hairs.
हिरण्यम् इव रोचते
hiraṇyam iva rocate (RigVeda 1.43.5)
Shining like the bright gold.
शुक्र इव सूर्यो
śukra iva sūryo (RigVeda 1.43.5)
Shines like the Sun
sthīrebhiraṃgai (RigVeda 2.33.9)
who is with firm limbs.
3) Revealing LordShip aspect of Lord Rudra:
The Lordship aspect of Lord Rudra is well revealed in SataRudriya section of YajurVeda in the 2nd Anuvakam. RigVeda also states many verses which states about LordShip aspect of Lord Rudra:
īśānādasya bhuvanasya (RigVeda 2.33.9)
who is Lord of the Universe.
bhuvanasya pitaram (RigVeda 6.49.10)
Father of the Universe.
न वा उ योषद् रुद्राद् असुरयम्
na vā u yoṣad rudrād asurayam (RigVeda 2.33.9)
The strength of Godhead never departs from Rudra.
satpatiṃ (RigVeda 2.33.12)
Lord of the Existence.
gāthapatiṃ (RigVeda 1.43.4)
Lord of the Hymns.
medhapatiṃ (RigVeda 1.43.4)
Lord of the sacrifice.
श्रेष्ठो देवानां वसुः
śreṣṭho devānāṃ vasuḥ (RigVeda 1.43.5)
Best among the Gods.
pururupa (RigVeda 2.33.9)
who has multiforms.
yajataṃ viśvarupam (RigVeda 2.33.10)
who has this whole universe as his form.
sugandhīm (RigVeda 7.59.12)
who is the essence (like sugandha is essence in flower).
puṣṭīvardhanam (RigVeda 7.59.12)
who is the cause of the growth of the Universe.
4) Revealing of grace seeking verses from Lord Rudra:
RigVeda reveals many verses which sing to Lord Rudra so that the sages can receive grace of Lord Rudra:
कद् रुद्राय प्रचेतसे मीड्हुष्टमाय तव्यसे। वोचेम शंतमं हृदे ।।
kad rudrāya pracetase mīḍhuṣṭamāya tavyase। vocema śaṃtamaṃ hṛde
What shall we sing to Rudra, strong, most bounteous, excellently wise, That shall be dearest to his heart?
क्व से ते रुद्र मृडयाकुर हस्तो
kva se te rudra mṛḍayākura hasto (RigVeda 2.33.7)
where is that gracious Hand of thine?
गीर्भिराभि रुद्रं दिवा वर्धया रुद्रमक्तौ
gīrbhirābhi rudraṃ divā vardhayā rudramaktau (RigVeda 6.49.10)
Rudra by day Rudra in night we honour with these songs.
महो महि सुष्टुतिम् ईरयामी
maho mahi suṣṭutim īrayāmī (RigVeda 2.33.8)
I utter forth mighty hymn of praises.
गृणीमसि त्वेषं रुद्रस्य नामः
gṛṇīmasi tveṣaṃ rudrasya nāmaḥ (RigVeda 2.33.8)
We sing the splendid name of Rudra.
कुमारश् चित् पितरं वन्दमानम् प्रति नानाम रुद्रोपयन्तम्
kumāraś cit pitaraṃ vandamānam prati nānāma rudropayantam (RigVeda 2.33.12)
I have surrendered myself to you as a boy to the respected father approaching.
5) Revealing of grace showing verses of Lord Rudra:
RigVeda also narrates many verses which shows how Lord Rudra graces to the devotees:
भिषक्तमं त्वा भिषजां शृणोमी
bhiṣaktamaṃ tvā bhiṣajāṃ śṛṇomī (RigVeda 2.33.4)
I hear you as the most curing among all curing.
हस्ते विभ्रद् भेषजा
haste vibhrad bheṣajā (RigVeda 1.114.5)
whose hand filled of sovran medicines.
वार्याणी शर्म वर्म छर्दिर
vāryāṇī śarma varma chardira (RigVeda 1.114.5)
grant us refugee, protection and shelter.
अपभर्ता रपसो दैव्यस्याभी
apabhartā rapaso daivyasyābhī (RigVeda 2.33.7)
Deliverer from defect of the Gods.
bṛhantamṛṣvamajaraṃ (RigVeda 6.49.10)
Great Blissfull and Immortal.
bhūrer dātāraṃ (RigVeda 2.33.12)
The giver of many.
mṛtyormukṣīya māmṛtā (RigVeda 7.59.12)
who provides immortality through Moksha.
6) Revealing of Desire of Rudra Consciousness:
RigVeda also reveals about state which sages seek where perfect thoughts of Lord Rudra comes to their mind. ie. Wishing of full mind devotion to Lord Rudra:
आ ते पितर मरुतां सुम्नम् एतु
ā te pitara marutāṃ sumnam etu (RigVeda 2.33.1)
May your perfect thought come to us Oh father of Maruts.
आ विवासेयं रुद्रस्य सुम्नम्
ā vivāseyaṃ rudrasya sumnam (RigVeda 2.33.6)
May perfect thought of Rudra comes in mind.